Drying substances, preparation and use thereof

ABSTRACT

There is provided herein a dryer polymer substance adapted to pervaporate a fluid (such as water, water vapor or both), the polymer substance includes: a porous support member having a plurality of pores, wherein at least a portion of the pores are filled with a cross-linked co-polymer comprising (i) a cationic monomer and an anionic monomer, (ii) a zwitterionic monomer, or a combination thereof. The substance may include a membrane or a tube. There is further provided herein a process for the preparation of a dryer polymer substance adapted to pervaporate a fluid (such as water, water vapor or both), the process includes impregnating into at least a portion of the pores of a porous support member a solution which comprises: (i) a cationic monomer and an anionic monomer, (ii) a zwitterionic monomer, or a combination of (i) and (ii), graft co-polymerizing the anionic monomer and the cationic monomer and/or the zwitterionic monomer within at least a portion of the pores to form a co-polymer, and cross-linking the co-polymer, such that the pores of the support member are at least partially grafted with a cross-linked co-polymer bound to the support member.

RELATED APPLICATIONS

Cross-reference is made to commonly-owned, co-pending (Ser. No. ______),filed on even date herewith.

FIELD

The invention relates to the field of membranes and other substratesexhibiting water pervaporation properties.

BACKGROUND

The separation or removal of liquids, such as water, from gases, such asorganic gases, is an important process within the chemical,petrochemical, medical and energy industries. Water removal is importantin the primary production of a wide range of organic solvents, in therecovery and recycling of used solvents, and in the removal of waterfrom chemical equilibrium reactions to drive the reaction towards apreferred product.

Another application that requires gas that is free or essentially freeof liquids, such as water, is medical breath analysis, which isperformed to provide information related to a patient's condition. Anexample of a gas analysis often performed is capnography, which is themonitoring of respiratory carbon dioxide (CO₂) concentration, usuallytime dependent. The time dependent respiratory CO₂ concentration may beused to directly monitor the inhaled and exhaled concentration of CO₂,and indirectly monitor the CO₂ concentration in a patient's blood. Othergases such as oxygen (O₂), carbon monoxide (CO), nitrogen or the likemay also be measured individually or in combination.

In breath analysis systems, for example capnography, breath gas can besampled such as by a mainstream or a sidestream analyzer. In mainstreamanalyzers, the sample chamber is positioned within the patient's gasstream, usually near the patient's end of the breathing system. Thisarrangement is normally heavier and more cumbersome than sidestreamsystems.

In sidestream analyzers, gas is often drawn from the breathing system bya tube. The tube, which may be connected to an adaptor, delivers the gasto a sampling place (such as a sampling chamber). It is preferable thatthe sampling line is clear of liquids, such as condensed out liquids, inthe fluid sample at all times, in order to permit continuous,non-interfered monitoring.

Condensed out liquids generally refer to water that condenses out fromthe humidity (the water vapor in breath) in the sampling tubes.Condensed out liquids are a major problem commonly hindering breathanalyses, particularly sidestream capnography. The internal humiditylevels in the tubes are high, especially in proximity to the breathcollection area, since the exhaled and inhaled breath is humid andrelatively warm. This is also the case in intubated patients who aregenerally artificially ventilated with gas (for example, air) having upto 100% humidity at a temperature normally above ambient temperature(for example, about 34° C.), depending on the airway humidificationsystem and patient needs. The humidity (water vapors) often condenses onthe inside of the tube, particularly as the tube extends farther fromthe breath collection area due to the temperature decreases.

Various processes that have been used to dehydrate fluids include newermembrane-based techniques such as pervaporation and vapor permeation.

Pervaporation is a process that involves a membrane in contact with afluid (which may include gas and/or liquid) on a feed or upstream sideand a vapor on the permeate or downstream side. Usually, a vacuum or aninert gas is applied on the vapor side of the membrane to provide adriving force for the process. Typically, the downstream pressure islower than the saturation pressure of the permeate. Vapor permeation isquite similar to pervaporation, except that a vapor is contacted on thefeed side of the membrane instead of a liquid. As membranes suitable forpervaporation separations are typically also suitable for vaporpermeation separations, use of the term “pervaporation” hereinencompasses both “pervaporation” and “vapor permeation”.

A variety of different types of membranes have been described for use inpervaporation dehydration processes. The materials used to prepare themembranes include hydrophilic organic polymers such as polyvinylalcohol,polyimides, polyamides, and polyelectrolytes. In addition, inorganicmaterials such as molecular sieves and minerals (for example, zeoliteswhich are aluminosilicate minerals) having a microporous structure havebeen used.

Initially, polymer-based pervaporation membranes comprised dense,homogeneous membranes. Typical examples of such membranes are describedby Yamasaki et al. [J. Appl. Polym. Sci. 60 (1996) 743-48], which isincorporated herein by reference in its entirety. These membranes sufferfrom low fluxes (amount of fluid that flows through a unit membrane areaper unit time) as they are fairly thick. While the flux of the membranescan be increased by decreasing the thickness of the membranes, thisleads to a decrease in mechanical strength and robustness.

Two routes have commonly been used to overcome the problem encounteredby the above membranes (some of which may be considered homogeneousmembranes). The first route involves the use of an asymmetric membranein which a dense surface layer is supported on a more porous materialmade from the same polymer. A typical example of such an asymmetricmembrane is disclosed by Huang et al. [Sep. Sci. Tech. 28 (1993)2035-48], which is incorporated herein by reference in its entirety.

A second route involves the formation of a dense thin film on thesurface of a suitable support membrane, wherein the chemical compositionof the dense surface layer and the supporting membrane are typicallydifferent. Typically, the support membrane is an ultrafiltrationmembrane that may contain an incorporated fabric to provide additionalstrength. Examples of these thin film composite membranes are describedin U.S. Pat. No. 4,755,299, U.S. Pat. No. 5,334,314, U.S. Pat. No.4,802,988 and EP 0,381,477. One major disadvantage of these thin-filmcomposite membranes, however, is their fragility. For example, thecommonly used cross-linked poly(vinylalcohol) films supported onpolyacrylonitrile ultrafiltration membrane supports are readily damagedthrough the formation of cracks in the films and through parts of thefilm falling away from the support. Great care must therefore be takenwhen mounting and using these membranes. It is also difficult to preparesuch membranes in such a way that they are free of defects.

A special form of the thin-film composite membranes is referred to as a“Simplex” membrane. These are made up of thin films using alternatinglayers of oppositely charged polyelectrolytes. The membranes are made bysuccessive immersions in solutions of the two differentpolylelectrolytes such that a multilayer complex is formed (see forexample Krasemann et al. [J. Membr. Sci. 150 (1998) 23-30]; Krasemann etal. [J. Membr. Sci. 181 (2001) 221-8], and Haack et al. [J. Membr. Sci.184 (2001) 233-43]), which are incorporated herein by reference in theirentirety. While a high selectivity and reasonable fluxes can be achievedwith the Simplex membranes, these membranes are complex to prepare, asthey require multiple coating steps. In order to get ideal performance,up to 60 dipping operations are sometimes needed. Another significantdrawback lies in the fact that these membranes cannot tolerate feedwater contents higher than 25% without loss of some of the multiplelayers.

Nafion® Membrane

A conventionally used way for dehydration of gases by pervaporation isusing proton conducting membranes, such as the membranes used in protonexchange membrane fuel cells. These membranes, an example of which issold under the brand name Nafion® by DuPont, are made of aperfluorinated sulfonic acid polymer. Nafion® membranes, which are fullyfluorinated polymers, have high chemical and thermal stability and arestable against chemical attack in strong bases, strong oxidizing andreducing acids, H₂O₂, Cl, H₂ and O₂ at temperatures up to about 100° C.Nafion® consists of a fluoropolymer backbone upon which sulfonic acidgroups are chemically bonded. However, although usually providingsufficient performance, Nafion® is an expensive material which rendersit economically unattractive in most applications.

Nafion® tubes have been used for breath analysis applications (such ascapnography), which, as discussed above, require an essentiallyliquid-free sampled gas. Nafion® tubes include, an inner tube coaxiallyfitted within the lumen of an outer tube. The inner tube, which isfabricated from a perfluorinated polymer, has a predetermined smallinternal diameter consistent with breath-by-breath response times. TheNafion® plastic employed exhibits high permeability to moisture (watervapor) but does not readily pass other respiratory gases, such as oxygenand carbon dioxide.

When used in breath analysis, Nafion® is a part of the patient's airwayand breath sampling system and thus cannot be transferred from onepatient to another and cannot even be re-used for the same patient. Thisdisposable nature of Nafion® increases the cost factor. The cost becomeseven more significant in applications that require relatively longNafion® tubes. For example, when sampling at 150 ml(milliliter)/minute(which is a common flow in capnography, for example), 6 inches ofNafion® are required. This length of Nafion® may cost at least an orderof magnitude more than the whole tubing system (such as a breathsampling system)

Because the Nafion® tubing in many applications has very thin walls(typically 0.002-0.003 inch), water permeates through it quickly. Thethin walls, however, also dictate a use of secondary structural supportsto prevent collapse of the walls. These structural supports complicatethe manufacture of the product and also reduce the water permeation.

The Nafion® tubing is fabricated by a process known as blown-filmextrusion. This process involves the following steps, which are akin tomaking trash bags, a material that has walls that are also far too thinto support their own weight. Typical trash bags have a wall thickness of0.002 or 0.003 inch (hefty trash bags may be a bit thicker). A typicalNafion® medical gas “line” tube is typically 0.0025 inch in wallthickness. And just as a trashcan holds the trash bag open, a meshinsert or an outer sleeve should be used to hold the tubing open fromthe inside or from the outside, respectively. The mesh may besufficiently coarsely woven so that it allows circulation of gases tothe surface of the tubing; however, as mentioned above, the presence ofthe mesh insert inside or outside the tube may interfere with theefficiency of the pervaporation process, typically reducing the waterpervaporation efficiency by over 50%. Another disadvantage of theNafion® is the chemically aggressive nature of the raw materials usedfor its preparation and the difficulty in the processing of thesematerials. For example, special extrusion means are required in order toallow processing of the Nafion®. Further, integrating Nafion® intotubing systems (such as breath sampling systems) is complicated andrequire special means.

There is thus a need for membranes and other substrates exhibiting waterpervaporation properties, which are effective, easy to handle andmanufacture and cost efficient.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods, which aremeant to be exemplary and illustrative, not limiting in scope. Invarious embodiments, one or more of the above-described problems havebeen reduced or eliminated, while other embodiments are directed toother advantages or improvements.

According to some embodiments, the present invention provides a robust,high-performance substance (such as a membrane or tube) designed for theselective removal of a polar fluid, such as water, from less polargases, such as air and CO₂, by a pervaporation process.

According to some embodiments, there is provided a dryer polymersubstance adapted to pervaporate a fluid (such as water, water vapor orboth), the polymer substance includes: a porous support member having aplurality of pores, wherein at least a portion of the pores are filledwith a cross-linked co-polymer including (i) a cationic monomer and ananionic monomer, (ii) a zwitterionic monomer, or a combination thereof.The substance may include a membrane or a tube.

According to some embodiments, there is provided a breath samplingsystem including a dryer polymer tube including a porous support memberhaving a plurality of pores, wherein at least a portion of the pores arefilled with a cross-linked co-polymer including (i) a cationic monomerand an anionic monomer, (ii) a zwitterionic monomer, or a combinationthereof, wherein the dryer polymer tube is adapted to pervaporate afluid (such as water, water vapor or both); and at least one of: aconnector adapted to connect the dryer polymer tube to a breath samplingtube and a reinforcement element. The connector, the reinforcementelement, or both may be molded with the dryer.

According to some embodiments, the porous support member may include atleast a partially hydrophilic support member, hydrophobic support memberor a combination thereof. The at least partially hydrophilic supportmember may include cellulose acetate (CA), poly(vinylidene floride)(PVDF), polysulfone (PSU), polyether sulfone (PES), Nylon 6,poly(ethylene-co-vinyl alcohol) (EVAL), poly(acrylonitrile) (PAN) or anyderivative thereof, or any combination thereof. The hydrophobic supportmember may include polypropylene, poly(tetrafluoroethylene) (PTFE),polyethylene (PE) or any derivative thereof, or any combination thereof.The anionic monomer may include an unsaturated carboxylic acid,unsaturated sulfonic acid or salts or anhydrides thereof, or acombination thereof. The anionic monomer may include2-acrylamido-2-methyl-1-propanesulfonic acid,3-allyloxy-2-hydroxy-1-propanesulfonic acid,2-methyl-2-propene-1-sulfonic acid, 2-propene-1-sulfonic acid, styrenesulfonic acid, vinylsulfonic acid or any combination thereof. Thecationic monomer may include an ammonium group (NH₄ ⁺), or a salt or aderivative thereof. The cationic monomer may include 4-vinylaniline,3-(acrylamidopropyl)trimethylammonium salt,(2-(acryloyloxy)ethyl](4-benzoylbenzyl)dimethylammonium salt,[2-(acryloyloxy)ethyl]trimethylammonium salt, diallyldimethylammoniumsalt, [3-(methacrylamido) propyl]trimethylammonium salt,[2-(methacryloyloxy)ethyl]trimethylammonium salt,vinylbenzyltrimethylammonium salt or any combination thereof. The molarratio of anionic monomer to cationic monomer in the cross-linkedcopolymer may be in the range of from 95:5 to 5:95. The molar ratio ofanionic monomer to cationic monomer in the cross-linked copolymer may bein the range of from 1:9 to 1:1. The zwitterionic monomer may include4-imidazoleacrylic acid, 4-aminocinnamic acid hydrochloride,4-(dimethylamino)cinnamic acid, 1-(3-sulfopropyl)-2-vinylpyridiniumhydroxide inner salt,3-sulfopropyldimethyl-3-methacrylamidopropylammonium inner salt,5-amino-1,3-cyclohexadiene-1-carboxylic acid hydrochloride or anycombination thereof.

According to some embodiments, the dryer polymer substance may include amembrane. According to some embodiments, the dryer polymer substance mayinclude a dryer tube.

The tube, according to some embodiments, may have a water evaporationrate of over 120 micro-liter/hour at a temperature of 22° C. and at 34%humidity, wherein the internal diameter of the tube is 1.0±0.1millimeter (mm); the outer diameter of the tube is 1.24±0.02 mm and thelength of the tube is 50 mm.

The tube, according to some embodiments, may have a water evaporationrate of over 150 micro-liter/hour at a temperature of 23° C. and at 55%humidity, wherein the internal diameter of the tube is 1.0±0.1millimeter (mm); the outer diameter of the tube is 1.24±0.02 mm and thelength of the tube is 50 mm.

The dryer tube may have an essentially circular internal cross-section.The dryer tube may have an essentially circular internal cross-sectionand a non-circular external cross-section. The dryer tube may have anon-circular internal cross-section and an essentially circular externalcross-section. The dryer tube may have a non-circular internalcross-section and a matching non-circular external cross-section.

According to some embodiments, the dryer polymer substance may include adryer tube, wherein the dryer tube may include an inner conduit, whereinthe internal cross-section of at least a portion of the inner conduit isessentially non-circular and adapted to collect liquids in proximity tothe inner walls of the inner conduit and thus allow an essentially freeof liquids flow in the dryer tube. The cross section of the innerconduit may be essentially similar to an n-point star, wherein n is aninteger having the value of between 2-10. The cross section of the innerconduit may be essentially similar to an n-petal flower, wherein n is aninteger having the value of between 2-10.

According to some embodiments, there is provided a process for thepreparation of a dryer polymer substance adapted to pervaporate a fluid(such as water, water vapor or both), the process includes:

impregnating into at least a portion of the pores of a porous supportmember a solution (or a mixture) which includes: (i) a cationic monomerand an anionic monomer, (ii) a zwitterionic monomer, or a combination of(i) and (ii);

graft co-polymerizing the anionic monomer and the cationic monomerand/or the zwitterionic monomer within at least a portion of the poresto form a co-polymer; and

cross-linking the co-polymer, such that the pores of the support memberare at least partially grafted with a cross-linked co-polymer bound tothe support member.

The process may further include surface-activating the porous supportmember prior to impregnation. The process may further includehydrophilization of the porous support member prior to impregnation. Theprocess may further include producing, by extrusion or molding, theporous support member prior to surface-activation.

According to some embodiments, the porous support member may include atleast a partially hydrophilic support member, hydrophobic support memberor a combination thereof. The at least partially hydrophilic supportmember may include cellulose acetate (CA), poly(vinylidene floride)(PVDF), polysulfone (PSU), polyether sulfone (PES), Nylon 6,poly(ethylene-co-vinyl alcohol) (EVAL), poly(acrylonitrile) (PAN) or anyderivative thereof, or any combination thereof. The hydrophobic supportmember may include polypropylene, poly(tetrafluoroethylene) (PTFE),polyethylene (PE) or any derivative thereof, or any combination thereof.The anionic monomer may include an unsaturated carboxylic acid,unsaturated sulfonic acid or salts or anhydrides thereof, or acombination thereof. The anionic monomer may include2-acrylamido-2-methyl-1-propanesulfonic acid,3-allyloxy-2-hydroxy-1-propanesulfonic acid,2-methyl-2-propene-1-sulfonic acid, 2-propene-1-sulfonic acid, styrenesulfonic acid, vinylsulfonic acid or any combination thereof. Thecationic monomer may include an ammonium group (NH₄ ⁺), or a salt or aderivative thereof. The cationic monomer may include 4-vinylaniline,3-(acrylamidopropyl)trimethylammonium salt,(2-(acryloyloxy)ethyl](4-benzoylbenzyl)dimethylammonium salt,[2-(acryloyloxy)ethyl]trimethylammonium salt, diallyldimethylammoniumsalt, [3-(methacrylamido) propyl]trimethylammonium salt,[2-(methacryloyloxy)ethyl]trimethylammonium salt,vinylbenzyltrimethylammonium salt or any combination thereof. The molarratio of anionic monomer to cationic monomer in the cross-linkedcopolymer may be in the range of from 95:5 to 5:95. The molar ratio ofanionic monomer to cationic monomer in the cross-linked copolymer may bein the range of from 1:9 to 1:1. The zwitterionic monomer may include4-imidazoleacrylic acid, 4-aminocinnamic acid hydrochloride,4-(dimethylamino)cinnamic acid, 1-(3-sulfopropyl)-2-vinylpyridiniumhydroxide inner salt,3-sulfopropyldimethyl-3-methacrylamidopropylammonium inner salt,5-amino-1,3-cyclohexadiene-1-carboxylic acid hydrochloride or anycombination thereof.

The process may further include, prior to impregnation, producing theporous support member in a tube form by extrusion or molding. The dryertube may have an essentially circular internal cross-section. The dryertube may have an essentially circular internal cross-section and anon-circular external cross-section. The dryer tube may have anon-circular internal cross-section and an essentially circular externalcross-section. The dryer tube may have a non-circular internalcross-section and a matching non-circular external cross-section.

According to some embodiments, the porous support member (of a dryerpolymer substance, such as a dryer tube) may include at least a firstsection having pores of a first diameter and a second section havingpores of a second diameter and wherein the first diameter is smallerthan the second diameter. The first section may be located at or inproximity to a first surface of the dryer polymer substance (such as aninner surface of the dryer tube) and the second section may be locatedat or in proximity to a second surface of a dryer polymer substance(such as an outer surface of the dryer tube).

According to some embodiments, the dryer polymer substance may include adryer tube, wherein the dryer tube may include an inner conduit, whereinthe internal cross-section of at least a portion of the inner conduit isessentially non-circular and adapted to collect liquids in proximity tothe inner walls of the inner conduit and thus allow an essentially freeof liquids flow in the dryer tube. The cross section of the innerconduit may be essentially similar to an n-point star, wherein n is aninteger having the value of between 2-10. The cross section of the innerconduit may be essentially similar to an n-petal flower, wherein n is aninteger having the value of between 2-10.

According to some embodiments, there is provided a method for thepreparation of tubing system adapted for water pervaporation, the methodincludes:

molding a porous support tube having at least one connector, at leastone reinforcement element or a combination thereof;

impregnating into at least a portion of the pores of a porous supporttube a solution (or a mixture) which includes: (i) a cationic monomerand an anionic monomer, (ii) a zwitterionic monomer, or a combination of(i) and (ii);

graft co-polymerizing the anionic monomer and the cationic monomerand/or the zwitterionic monomer within at least a portion of the poresto form a co-polymer; and

cross-linking the co-polymer, such that the pores of the support tubeare at least partially grafted with a cross-linked co-polymer bound tothe support member.

The method may further include surface-activating the porous supporttube prior to impregnation. The process may further includehydrophilization of the porous support member prior to impregnation.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thefigures and by study of the following detailed descriptions.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a flowchart describing a general process of production of adryer polymer substance, according to some embodiments;

FIG. 2 shows a flow for a process protocol of production of a dryerpolymer substance, according to some embodiments;

FIG. 3 shows a graph of the effect of temperature and the degree ofcrystalline (% crystalline) on the degree of grafting (% DOG), accordingto some embodiments;

FIG. 4 shows a flowchart describing a general process of production of adryer polymer substance, according to some embodiments;

FIG. 5 shows a flowchart describing a general process of production of adryer polymer substance, according to some embodiments;

FIG. 6 shows a flow for the process protocol of production of a dryerpolymer substance according to some embodiments;

FIGS. 7 a-d show exemplary dryer tubes, according to some embodiments;

FIG. 7 e shows an asymmetric porous dryer tube, according to someembodiments; and

FIGS. 8 a-c show longitudinal cross-sections of dryer tubes connected totubing systems, according to some embodiments.

DETAILED DESCRIPTION

In the following description, various aspects of the invention will bedescribed. For the purpose of explanation, specific configurations anddetails are set forth in order to provide a thorough understanding ofthe invention. However, it will also be apparent to one skilled in theart that the invention may be practiced without specific details beingpresented herein. Furthermore, well-known features may be omitted orsimplified in order not to obscure the invention.

According to some embodiments of the invention, there is provided apolymer substance, such as, but not limited to, a membrane or a tube,(such as a micro-tube) adapted to dry a gas (such as air, oxygen (O₂),oxygenated air, carbon monoxide (CO), carbon dioxide, (CO₂) or any othergas) from fluids, such as polar fluids, for example, water and/or watervapors. The polymer substance may further be adapted to allow flow ofthe gas (along the membrane or through the tube), while essentiallymaintaining the concentrations of other gas components (such as carbondioxide, CO₂, oxygen, nitrogen or any other gas).

The polymer substance may be adapted to be incorporated in samplingand/or analyzing systems, such as in a breath test analysis system. Inbreath test analysis, (particularly in side stream breath test analysis)exhaled breath is sampled from a subject and passed through a tubingsystem to an analyzer which provides information regarding thecomposition of the gas sample and/or characteristics and/or behavior ofany of the gas components (for example CO₂). In order to obtain accurateanalysis of the exhaled gas, the breath sample should maintain theinitial composition and characteristics of certain components but shouldalso be essentially free of water. The polymer substance, according tosome embodiments of the invention, is adapted to dry the sampled gasfrom water molecules while essentially maintaining the composition andproperties of other components which are essential for the analysis.According to some embodiments, the polymer substance may also be adaptedto wet a gas. For example, in a case of a tube or a membrane, on oneside of the tube or membrane the gas is dried, and on the other side thegas is wetted.

According to some embodiments, the polymer substance may exhibitpermeability for a fluid that is dependent on the polarity of the fluid,wherein the permeability increases with increasing polarity. Forexample, the polymer substance may exhibit better permeability to water(which is a polar compound) than to CO₂, which is an essentiallynon-polar compound.

According to some embodiments, the term “permeability” may refer to theability of a material (such as a polymer substance, for example, amembrane or a tube) to transmit (permeate) fluids (such as water and/orwater vapors).

According to some embodiments, the term “polarity” may refer to adipole-dipole intermolecular force between a positively-charged (even asmall positive charge) end of a molecule to a negative (even a smallnegative charge) end of another or the same molecule.

According to some embodiments, the polymer substance may exhibitpervaporation capabilities (such as pervaporation of water and/or watervapors pervaporation).

According to some embodiments of the invention, the term “pervaporation”may refer to a process that includes the transfer of fluid(s) through amembrane (such as the walls of a dryer polymer tube) wherein thefluid(s) enter the non-porous or porous membrane as vapor or liquid andpermeate through the membrane as vapor. The fluid(s) may include water,humidity, water vapor or other fluid such as methanol or any otherfluid.

The polymer substance, according to some embodiments of the invention,may be used instead of the Nafion® and may also exhibit better (oressentially similar) water pervaporation performance than the Nafion®.Better water pervaporation may include a faster transfer of waterthrough the material, at selected operating parameters.

According to some embodiments, (dryer) polymer substances used for gasdrying (or wetting) purposes should be adapted to allow pervaporation offluids (such as water and/or water vapors) but also to substantiallymaintain acceptable mechanical properties (such as strength andflexibility). According to some embodiments, the polymer substance maybe adapted to substantially maintain one or more of its initialdimensions (for example, its dimensions prior their use inpervaporation). According to other embodiments, the polymer substancemay be adapted to change one or more of its initial dimensions. Forexample, one or more of the dimensions of a polymer substance may change(for example, grow) during or after its use in pervaporation of fluids.For example, the thickness and/or the length of a membrane and/or a tubemay grow when fluid(s) are passed through.

According to some embodiments, the polymer substance may be adapted tobe robust in active environments, such as in breath sampling tubes,through which the patient may exhale or inhale medications or otheractive materials.

According to some embodiments, there are provided three main types ofpolymer substance, such as the polymer substance membranes or tubes,which are prepared by three main routes: The “grafting (dense) route”,the “blend (dense) route” and the “porous route”. According to someembodiments, the polymer substances provided herein, are adapted to beeasily manufactured and handled, resistant, structurally stable, and/oreasily integrated into the desired systems such as membrane systems ortubing systems.

A) Dryer Polymer Substance—the “Grafting (Dense) Route”

According to some embodiments, there is provided a dryer polymersubstance, such as, but not limited to, a membrane or a tube, comprisinga polymer grafted with a compound having group(s), such as aromaticgroup(s), for example, phenyl group(s), which group(s) is (are) capableof being sulfonated. An example of such a group may include styrene orany derivative thereof. According to some embodiments, the dryer polymersubstances may also include any material that is adapted to produceselective water (vapor or liquid) transport, particularly, but notlimited to sulfonic group type groups (or any derivative or saltthereof). An example of such dryer polymer substance is poly(vinylidenefluoride)-graft-poly(styrene sulfonated acid) (PVDF-g-PSSA) copolymer.

The term “aromatic group” may include, according to some embodiments,conjugated ring(s) of unsaturated bonds, lone electron pairs, and/orempty orbitals exhibiting a stabilization stronger than would beexpected by the stabilization of conjugation alone.

The term “sulfonic group” may include, according to some embodiments,any group, compound (such as an anion) having a sulfonic acid residue(—S(═O)₂—OH) or any salt (such as R—S(═O)₂—ONa) or derivative thereof.

The term “phenyl group(s)” (may also be referred to as a phenyl ring oras -Ph) may include, according to some embodiments, any group of atomshaving the formula —C₆H₅ or any derivative thereof. According to someembodiments, the term “phenyl group(s)” may cover unsubstituted orsubstituted phenyl group(s).

The term “styrene” (may also be referred to as vinyl benzene, cinnamene,styrol, ethenylbenzene, phenethylene, phenylethene, as well as othernames), is an organic compound with the chemical formula C₆H₅CH═CH₂.

The term “polymer” may include, according to some embodiments, anymolecule composed of repeating structural units connected to each other,typically, by covalent chemical bonds. The term “polymer” may include,according to some embodiments, a homopolymer (which is a polymer derivedfrom one monomer species), a copolymer (which is a polymer derived fromtwo (or more) monomeric species) or a combination thereof. A polymer, asreferred to herein, may include a mixture of polymers. A polymer, asreferred to herein, may include linear and/branched polymers whichconsist of a single main chain with one or more polymeric side chains.

The terms “grafted” or “grafting” may include, according to someembodiments, bonding (for example covalently bonding) to a polymer or aco-polymer, a compound (such as a monomer compound) to produce a polymeror a co-polymer containing bonded compounds (a grafted polymer). Anexample of a grafted polymer may include a polymer grafted with sidechains that has a different composition or configuration than the mainchain of the polymer. A more specific example of grafting may include aprocess wherein styrene monomers are introduced and bonded to a polymer(such as poly vinylidene fluoride (PVDF)) to produce poly(vinylidenefluoride)-graft-polystyrene (PVDF-g-PS) copolymer.

A copolymer, as referred to herein, may include an alternatingcopolymer, a periodic copolymer, a random copolymer, a block copolymeror any combination thereof.

The term “dryer polymer substance” may include, according to someembodiments, any substance, including but not limited to, a tube or amembrane, that comprises at least one polymer, wherein the substance isadapted to perform pervaporation.

Examples of polymers may include polyolefins (such as polypropylene,polyethylene and copolymers thereof) and/or fluoro-polymers, forexample, poly vinylidene fluoride (PVDF) or any other fluoro-polymersuch as those which may be found in http://solutions.3m.com/wps/portal/3M/en_US/dyneon_fluoropolymers/Home/Products_and_Solutions/Products/Fluoroplastics/PVDF,which is incorporated herein by reference.

PVDF may include PVDF (homopolymer) and PVDF (copolymer). PVDF(homopolymer) may include poly(vinylidenfluoride) of 1,1-fluoro-ethene.The chemical structure of PVDF (homopolymer) is —[CF₂—CH₂]_(n)—, whereinn is an integer greater than 1.

PVDF (copolymer) may include HFP (hexafluoropropylene)-PVDF copolymerhaving a chemical structure of —[CF₂—CH₂]_(x)—[CF₂—CF(CF₃)]_(y)— whereinx and y are, independently, integers.

The nature and characteristics of the polymer (such as PVDF) beinggrafted affect the performance and characteristics of a dryer polymersubstance. For example, the percentage of grafting of a polymer (such aspolyvinylidene fluoride (PVDF) with styrene related compound, or anyother suitable compound) may be affected by the degree of crystallinityof the polymer. For example, for a polymer having a lower degree ofcrystallinity (such as PVDF copolymer), grafting may easily be performedcompared to a polymer having a higher degree of crystallinity (such asPVDF homopolymer). The degree of grafting (such as styrene grafting,which may also be referred to as styrenization) of a polymer is relatedto the amount of the sulfonic acid groups (or any derivative or saltthereof) that can be bound to the grafted polymer. The more styrenecompounds in the polymer, the more sulfonic acid groups may be bound.The sulfonic acid groups, as mentioned hereinabove, have a high affinityfor water and thus determine the pervaporation characteristics of thedryer polymer substance (of course other factors may also influence thepervaporation characteristics of the dryer polymer substance as well).According to some embodiments, the terms “crystalline” may refer to asolid, such as a polymer, having a structural order. Structural ordermay include molecules arranged in a regular, periodic manner.Crystallinity, the structural order in a solid, may be detected forexample, by diffraction techniques. Materials (such as polymers), caninclude crystalline and amorphous (a solid showing no long-range orderof the positions of the atoms/molecules) regions. According to someembodiments, the term “degree of crystallinity” may refer to thefractional amount (by volume or by mass) of crystallinity in a polymersample. A “crystalline polymer” may include a polymer showingcrystallinity, at least in some region(s) thereof.

Different formulations (for example different ratios ofhomopolymer/copolymer) may be used in order to optimize the degree ofcrystalinity and thus the degree of grafting, sulfonation andpervaporation performance of the dryer polymer substance. The ratio ofhomopolymer/copolymer may also affect the mechanical properties and/orability to undergo extrusion. For example, a polymer substance producedusing a mixture containing about 25% homopolymer with 75% copolymer willexhibit a moderate degree of grafting capability with stiffer structure,compared, for example, to 100% copolymer.

According to some embodiments, grafting (such as styrenization)temperature and styrenization duration also affect the performance andcharacteristics of the dryer polymer substance.

According to some embodiments, the percentage of grafting (for examplestyrenization) may be in the range 20-50% (wt), for example, 25-40%(wt), and more specifically 33% (wt). According to some embodiments, thestyrenization (grafting) temperature may be in the range of 20° C.-70°C., more specifically, 25° C.-60° C., for example 25° C., 40° C. or 55°C. According to some embodiments, the styrenization includes immersionin 50%-100% styrene (for example 80% styrene in methyl benzene).

After grafting the polymer, sulfonation is being conducted in order tocreate the pervaporation characteristics of the polymer substance.

The dryer polymer substance may be produced by modification ofpoly(vinylidene fluoride) (PVDF), for example, PVDF homopolymer,copolymer or both) by irradiation, such as ‘gamma’ irradiation, followedby chemical treatment of the PVDF infrastructure, incorporating graftsof styrene and then introducing sulfonic acid groups to performsulfonation of the polystyrene groups. The product of such process ispoly(vinylidene fluoride)-graft-poly(styrene sulfonated acid)(PVDF-g-PSSA) copolymer.

Reference is now made to FIG. 1, which illustrates a flowchart 100describing a general process of production of a dryer polymer substance.Step 110 includes obtaining a polymer (for example, in a solid form,such as powder, particulate or pellet) or a polymer mixture/formulation,for example, PVDF homopolymer, copolymer or a combination thereof). Step120 includes processing the polymer, for example, by extrusion or bymolding (such as injection molding) to produce the desired structure ofpolymer substance 130 (for example, a polymer tube or membrane). Thepolymer formulation and the processing of the polymer eventuallydetermine the level of crystallinity of the polymer substance 130. Step140 includes the activation of the polymer substance 130 whichfacilitates the grafting in the following step. Activation, whichaffects the bulk of the substance, may be performed by irradiation ofthe polymer substance 130 (for example, tube or membrane) or chemicalactivation using, for example, peroxides. The irradiation, typicallygamma radiation, forms terminals (carbon radicals formed by hydrogenatoms removal) to which styrene groups will be bound in the next step.Step 150 includes grafting of a compound having a group which is adaptedto be solfonated. Such compound may be a monomer that includes styrene,wherein the styrene is adapted to be sulfonated. This process, whichincludes grafting of styrene monomers into the polymer, may also bereferred to as styrenization. The styrene monomers bind to the terminalsformed in step 140. The grafting step (step 140), such as thestyrenization step, is performed at a predetermined temperature ortemperature gradient and for a predetermined duration, which, togetherwith the level of crystallinity of the polymer substance 130, determinesthe level of styrenization. This step also includes the polymerizationof the compounds adapted to be sulfonated (such as styrene monomers) toform a polymer (such as polystyrene). Step 160 includes the sulfonationof the compounds adapted to be sulfonated, such as the styrene groups,to produce a dryer polymer substance 170. Flowchart 100 shows a processfor producing a dryer polymer substance 170, which may include a dryertube or membrane. As can be seen in flowchart 100, step 120, whichincludes processing of the polymer (for example by extrusion or bymolding), is conducted prior to the steps of irradiation (step 140),styrenization (step 150) and sulfonation (step 160). It was surprisinglyfound that conducting the steps of irradiation (step 140), styrenization(step 150) and sulfonation (step 160) prior to processing the polymer(step 120) limits the amount of styrene and sulfonic acid groups thatcan be added to the polymer. In other words, when styrenization andsulfonation exceed a certain level, processing (for example, extrusion)is very problematic and often impossible. According to some embodimentsof the invention, processing the polymer (for example, by extrusion orby molding) is conducted prior to the steps of irradiation (step 140),styrenization (step 150) and sulfonation (step 160). This order mayallow increasing the styrene/sulfonic acid percentage in the polymer andthus increasing the pervaporation performance of the dryer polymersubstance. Known drying substances, such as Nafion®, are extruded afterthe styrene sulfonic acid is already present in Teflon® (as copolymerwith perfluorovinyl ether sulfonate). This limits the amount ofstyrene/sulfonic acid that could be present in Nafion®, (as the moreperfluorovinyl ether sulfonate groups added the harder it is to process)and thus limit the pervaporation performance thereof. In addition, inthe case of Nafion®, performing the extrusion after the styrene sulfonicacid is already present in the copolymer results in a more complicatedextrusion process, for example, processing temperatures are high(typically 300° C.) and special equipment is required to avoid damagecaused by the “aggressive” Nafion® chemicals. It is noted thatprocessing of the polymers disclosed herein (such as PVDF) is, accordingto some embodiments, easy and does not require special conditions as inthe Nafion® processing. In addition, polymers like PVDF are basic andnon-expensive as opposed to the Nafion® materials.

According to some embodiments, when the polymer is processed to producethe desired structure of the polymer substance (such as a tube) by wayof molding, several advantages may be accomplished. The molding processmay improve the integration of the dryer polymer substance within thedesired systems and at the same time also improve the mechanicalproperties of the substance. For example, one or two connectors,structural support and/or reinforcement elements (such as ribs) or anyother feature can be molded with the dryer tube. In addition, by theprocess of molding, any shape can be formed from the polymer(s)compounds, for example, a breath sampling cannula.

Reference is now made to FIG. 2, which illustrates a scheme describingan example of a process protocol of production of a dryer tube(including grafting procedure) in a process that may be called a“grafting (dense) route”. Step 1 describes obtaining PVDF as rawmaterial and performing an extrusion procedure at 230° C. at acontrolled draw down ratio, to produce a PVDF tube (of course, othersubstances other than a tube, such as membranes, for example, can alsobe produced in a similar way). In Step 2, the PVDF tube is sealed in aninert atmosphere (such as under nitrogen or helium) and irradiated bygamma radiation at 2.5 Mrad dose at low temperature to produce anirradiated PVDF (i-PVDF) tube. Step 3 describes the incorporation ofgrafts of polystyrene in the i-PVDF tube. The i-PVDF tube is refluxed instyrene (100%) at 55° C. for 24 hours, washed by Soxhlet in toluene for8 hours, and then washed in ethanol at room temperature (RT), which isgenerally 25° C., to produce a PVDF-graft-polystyrene (PVDF-g-PS) tube.Step 4 describes the sulfonation of the polystyrene groups on thePVDF-g-PS tube. The PVDF-g-PS tube is immersed in 0.5 Molar (M)chlorosulfonic acid in dichloroethane for 24 hours at RT, the product isthen washed with dichloroethane and distilled water for 2 hours. Thisstep yields an unneutralized poly(vinylidenefluoride)-graft-poly(styrene sulfonated acid (PVDF-g-PSSA) tube, whichis then neutralized, in step 5, by hydrolization in 0.5 M KOH for 16hours at RT.

A comparative study was performed in order to assess the performance ofthe PVDF-g-PSSA tube and compare it to the performance of the Nafion®tube. The results of this study are summarized in Table 1 below.

TABLE 1 Performance of the PVDF-g-PSSA tubes compared to the performanceof the Nafione ® tube. RH (relative Tem- ambient PVDF-g- Neutralizedperature humidity) PSSA PVDF-g- Test [c.] [%] tube PSSA tube Nafion ®Water 22 34 261.5 395.5 22 uptake [%] Leak 22 34 10.08 10.08 10.08[μL/hour] ΔCO₂ 23 55 1 1 1 Water 22 34 292 352 155 evaporation [μL/hour]Vapor 22 34 No No 151 penetration evidence evidence [μL/hour] of waterin of water in the trap the trap

For the tubes tested herein: the internal diameter: 1.0±0.1 millimeter(mm); the outer diameter: 1.24±0.02 mm; length 50 mm.

As shown in Table 1, the following five factors were assessed for eachtype of tube (PVDF-g-PSSA, neutralized (such as Na) PVDF-g-PSSA andNafion®):

-   -   1. Water uptake [%];    -   2. Leak [micro-liter/minute];    -   3. ΔCO₂ (change in carbon dioxide)    -   4. Water evaporation [micro-liter/hour]; and    -   5. Water vapor penetration [micro-liter/hour].

These five factors were tested at the specified temperature [° C.] andrelative ambient humidity (RH) [%].

Water uptake measurements were performed by immersing a tube indistilled water at RT for 24 h (or 2 h in boiling water) and checkingweight increase [%]. The larger the increase, the more water the tube iscapable of absorbing.

Leak measurements were performed by connecting the tube to adifferential manometer, creating vacuum in the tube and monitoring thepressure change with time. The results, which are translated intomicro-liter/minute, indicate the performance of the tube in blockinggases, such as air, from entering or exiting the tube. As mentionedherein, a tube having good gas blocking characteristics is preferredsince it maintains the concentrations of gas elements duringmeasurement.

ΔCO₂ measurements were performed by flowing CO₂ at a known concentration(for example 5%) through a measurement device with and without amembrane (such as a tube membrane) and comparing the CO₂ concentrationat the measurement. The difference between the two CO₂ concentrationreadings (with and without the membrane) is indicative of the amount ofCO₂ that leaked out or “escaped” from the system.

Water evaporation measurements were performed by trapping water in aclosed tube and weighing the tube after certain time periods. Thedecrease in weight is indicative of water evaporation from the tube.

Water vapor penetration measurements were performed by flowing humid gasat 35° C. through a tube and trapping the remaining condensed out water(if left) in a trap. The amount of water in the trap is indicative ofthe amount of water vapor the tube did not absorb/pervaporate. In otherwords, the more water in the trap, the more water vapor the tube did notabsorb/pervaporate.

The following was surprisingly found (as summarized in Table 1):

-   -   The PVDF-g-PSSA tubes show significantly better (higher) water        uptake than the Nafion® tube.    -   The PVDF-g-PSSA tubes show better (higher) water evaporation        rate than the Nafion® tube.    -   The PVDF-g-PSSA tubes show better water vapor penetration        performance compared to the Nafion® tube (zero evidence to water        vapor penetration as opposed to 151 [micro-liter/hour] in the        Nafion® tube).    -   At the same time it was found that the PVDF-g-PSSA tubes do not        show any decline in the CO₂ barrier properties. In other words,        essentially no loss of CO₂ from the tube is evident during use,        and therefore the PVDF-g-PSSA tubes can be used for CO₂        analysis, for example, in breath tests.

As can be seen from Table 1 above, the PVDF-g-PSSA tubes (in its twoversions, neutralized and non-neutralized) demonstrate better waterpervaporation results than the Nafion® tube. Furthermore, a leak testwas carried out continuously every single hour, simultaneous with thevapor penetration test. The leak of the PVDF-g-PSSA tubes was found tostay almost zero, even after 8 hours of the vapor test. In other words,the PVDF-g-PSSA tubes facilitate water pervaporation while at the sametime maintain other gas components, such as CO₂, and therefore allowreliable gas (such as breath) analysis.

Although neutralized (for example, Na neutralized, such as by use ofSO₃Na) PVDF-g-PSSA tubes show better water permeability than thenon-neutralized PVDF-g-PSSA tubes, both of the two show adequateperformances for the gas (for example, breath) dryer tube application.On the other hand, the non-neutralized PVDF-g-PSSA tubes exhibit bettermechanical behavior than the Na PVDF-g-PSSA tubes.

Furthermore, under humidity conditions, the PVDF-g-PSSA tubes absorbedcertain amounts of water, which in turn improved their mechanicalbehavior (for example, an increase in flexibility). Considering thesuperior mechanical behavior and the fact that both types show similarperformances in the vapor penetration test, the non-neutralized membranemay be found to be more favorable, according to some embodiments.

One of the key parameters that control the degree of grafting is thedegree of crystallinity. The more crystalline the PVDF copolymer is, theless its capability to absorb styrene monomer, which participated in thegrafting process. Control of the crystallinity can be done whilealtering the material formulation with respect to crystallizationsensitivity: for example, homopolymer or co-polymer or mixture(s)thereof, and while altering the cooling rate with different coolingmedium: for example, water, air, oil and medium temperature. Table 2below shows the results (including the dimensional stability in thechemical reaction and during the pervaporation action) for PVDF-g-PSSAtubes made from copolymer, homopolymer or mixture(s) thereof. Thestyrenization reaction took place at 55° C. and also at room temperature(25° C.).

TABLE 2 Performance of differently prepared types of PVDF-g-PSSA tubescompared to the performance of PVC and Nafion ® tubes. PVDF-g- PVDF-g-PVDF-g- PVDF-g- PVDF-g- PSSA tube PSSA tube PSSA tube PSSA tube PSSAtube PVC (copolymer (copolymer (homopolymer (homo and copo (homo andcopo Test tube Nafion ® at 55° C.) at 25° C.) at 55° C.) at 55° C.) at25° C.) Degree of — — 132 60 30 35 28 grafting [%] Water uptake — 22 26060 15 65 22 [%] Leak 0 0-10 0-10 0-10 0-10 0-10 0-10 [μL/min] ΔCO₂ —  11 1 1 1 1 Water — 155  260 230 43 155 102 evaporation [μL/hour] Vapor433 (0) 151 (282) No evidence 145 (288) 305 (128) 159 (274) 194 (239)penetration of water in [μL/hour] the trap (the Δ from PVC) Change in —— 146 60 6 45 12.5 thickness due to chemical reaction[%] Change in — —97 60 9 37 15 diameter due to chemical reaction[%] Change in — — 42 36 325 11 thickness due to pervaporation action[%] Change in — — 15 14 3 1310 diameter due to pervaporation action[%]

Table 3 summarizes experimental results for a polyvinyl chloride (PVC)tube and six types of PVDF-g-PSSA tubes:

-   -   1. PVDF-g-PSSA copolymer wherein styrenization was conducted at        55° C.;    -   2. PVDF-g-PSSA copolymer wherein styrenization was conducted at        25° C.;    -   3. PVDF-g-PSSA homopolymer wherein styrenization was conducted        at 55° C.;    -   4. PVDF-g-PSSA homo and copolymer wherein styrenization was        conducted at 55° C.;    -   5. PVDF-g-PSSA homo and copolymer wherein styrenization was        conducted at 25° C.; and    -   6. Nafion®.

The following ten factors were assessed:

-   -   1. Degree of grafting [%];    -   2. Water uptake [%];    -   3. Leak [micro-liter/minute];    -   4. ΔCO2 (change in carbon dioxide);    -   5. Water evaporation [micro-liter/hour];    -   6. Water vapor penetration [micro-liter/hour] and the Δ        (difference) from the PVC measurement;    -   7. Change in thickness due to chemical reaction (styrenization        and sulfonation) [%];    -   8. Change in diameter due to chemical reaction (styrenization        and sulfonation) [%];    -   9. Change in tube thickness due to pervaporation action [%]; and    -   10. Change in tube diameter due to pervaporation action [%].

These parameters were measured at a temperature of 23° C. and relativeambient humidity (RH) of 50%.

The following was surprisingly found:

The water uptake of the following tubes was similar to or higher thanthat of the Nafion®:

PVDF-g-PSSA copolymer wherein styrenization was conducted at 55° C.,PVDF-g-PSSA copolymer wherein styrenization was conducted at 25° C.,PVDF-g-PSSA homo and copolymer wherein styrenization was conducted at55° C. and PVDF-g-PSSA homo and copolymer wherein the styrenization wasconducted at 25° C.

The water evaporation of the following tubes was similar to or higherthan that of the Nafion®:

PVDF-g-PSSA copolymer wherein styrenization was conducted at 55° C.,PVDF-g-PSSA copolymer wherein styrenization was conducted at 25° C. andPVDF-g-PSSA homo and copolymer wherein styrenization was conducted at55° C.

At a lower grafting temperature, such as 25° C., the degree of graftingreached a lower level (which may also results in lower amount ofsulfonic groups) compared to the degree of grafting achieved under 55°C. Still, even at a lower grafting temperature, such as 25° C., theperformances of the tubes were acceptable for water pervaporationpurposes, and in some cases (PVDF-g-PSSA) tube (copolymer at 25° C.) theperformances were far better than the Nafion's.

In accordance with an additional/alternative embodiment of theinvention, there is provided herein a method of monitoring and/orcontrolling the degree of grafting of polystyrene. This may beaccomplished, for example, by adjusting the PVDF material combinationbetween copolymer and homopolymer, changing (for example, reducing) theduration of polystyrene anticipating and grafting process and/oraltering/optimizing the cooling procedure during the tube manufacturingin extrusion (for example, Step 1 of FIG. 2). Reference is now made toFIG. 3, which shows a scheme describing how the temperature of thereaction and the degree of crystallinity (% crystalline) may control thedegree of grafting (% DOG). The degree of grafting (% DOG) increaseswith the decrease in the degree of crystallinity (% crystalline).Raising the temperature increases the degree of grafting (% DOG) for agiven degree of crystallinity (% crystalline).

Depending on the case and purpose, a specific dryer polymer substanceand manufacturing conditions may be chosen. In accordance with anadditional/alternative embodiment of the invention, there is providedherein a method for controlling the performance (for example, wateruptake, water vapor penetration or any other type of performance) of aPVDF-g-PSSA tube by determining the tube's length.

According to some embodiments, the grafting may be performed in specificareas of the polymer substance, while other areas may remain un-grafted(for example, but not limited to, by blocking arrears of the polymersubstance where grafting is not desired). Accordingly, the polymersubstances covered under the scope of some embodiments of thisinvention, may include a polymer substance that comprises grafted areas(for example, grafted with PSSA, and un-grafted areas). This may allow,for example, control of the pervaporation performance of a dryer polymersubstance, but may be used for any other application.

Mechanical Properties of Gas Dryer Tubes

Table 3 below shows mechanical properties of PVDF-g-PSSA tube comparedto the mechanical properties of a Nafion® tube.

The mechanical properties detailed in the table below were taken fromoutput of tensile test carried out on tube samples with an Instronuniversal testing machine according to ASTM D638 at a tension rate of 25mm/min. All values in the table are normalized for purposes ofcomparison.

TABLE 3 mechanical properties of PVDF-g-PSSA tube compared to themechanical properties of a Nafion ® tube. Ultimate tensile Young'sModulus Ultimate elongation Tube sample type strength [MPa] [MPa] [%]Nafion ® tube 20.2 152.8 81 PVDF-g-PSSA 25.6 281.3 362 tube (copolymerat 55° C.)

The term “ultimate tensile strength” may refer to, according to someembodiments, the stress (the average amount of force exerted per unitarea) at which a material breaks or permanently deforms. Tensilestrength is a bulk property and, consequently, does not depend on thesize (such as length or width) of the test specimen (such as tube). Theultimate tensile strength is normalized to the wall thickness.

The term “Young's modulus” may refer to, according to some embodiments,a measure of the stiffness (the resistance of an elastic body todeformation by an applied force) of an elastic (such as isotropic)material. The Young's modulus is normalized to the wall thickness.

The term “ultimate elongation” may refer to, according to someembodiments, the percentage of stain to rapture.

It can be seen from Table 3 that the PVDF-g-PSSA tube is tougher,stiffer and less brittle compared to the Nafion® tube.

B) Gas Dryer Membrane—the “Blend (Dense) Route”

According to some embodiments, there is provided a dryer polymersubstance comprising a hetero-phase polymer composition comprising twoor more polymers, wherein at least one of the two or more polymerscomprises sulfonic groups, wherein the substance has a permeability fora fluid that is dependent on the polarity of the fluid, wherein thepermeability increases with increasing polarity. For example, thepolymer substance may exhibit better permeability to water (which is apolar compound) than to CO₂, which is an essentially non-polar compound.

The term “hetero-phase polymer” or “hetero-phase polymer composition”may refer to the presence of at least two phases: a continuous or matrixphase and another phase which is a dispersed phase distributed withinthe matrix phase. The dispersed phase may be discontinuous (such asdispersed islands) or may be a co-continuous phase (such as whereindispersed islands coalesce into larger islands).

According to some embodiments, the term “co-continuous phase” structuremay refer to two or more phases intertwining in such a way that bothphases remain substentially continuous throughout at least a portion ofthe material. The morphology may be analogous to that of a sponge soakedin water where both sponge and water form continuous systems.

According to some embodiments, there is provided a dryer polymersubstance, such as, but not limited to, a membrane or a tube, comprisingtwo or more polymers having an essentially hetero-phase structure (forexample, a co-continuous phase structure), wherein at least one of thetwo or more polymers comprising group(s), such as phenyl group(s), whichgroup(s) is (are) capable of being sulfonated. An example of such groupmay include styrene or any derivative thereof. Such polymers mayinclude, for example, polystyrene (PS) and/or styrene copolymer, suchas, styrene-ethylene-butylene-styrene (SEBS) or any derivatives thereof.

According to some embodiments, the dryer polymer substances also includeany material that is adapted to produce selective water (vapor orliquid) transport, particularly, but not limited to, sulfonic acid typesubstances. Examples of such dryer polymer substances arepoly(vinylidene fluoride)/polystyrene sulfonated acid (PVDF/PSSA) andpoly(vinylidene fluoride)/styrene-ethylene-butylene-styrene sulfonicacid (PVDF/SEBS-SA). Other polymers which may be used instead of or inaddition to the PVDF include polypropylene-homopolymer (PP-homo),polypropylene-random copolymer (PP-raco), medium density polyethylne(MDPE) or any other appropriate polymer. According to some embodiments,at least one of the polymers which form the hetero-phase structure (suchas PVDF) create It is noted that the sign “/” (forward slash) betweentwo polymers indicates that the two polymers are adapted to form or areessentially forming a hetero-phase phase structure (such as aco-continuous phase structure). It is distinguished from the sign “g”(graft) between two polymers, which indicates that one of the polymersis grafted in the other polymer.

According to some embodiments, the dryer polymer substances may beproduced by physically blending two or more polymers and/or copolymers(such as PVDF with polystyrene (PS) and/or styrene copolymer, such asstyrene-ethylene-butylene-styrene (SEBS)) with a compatibilizing agent,followed by the formation of a desired form, such as a tube or amembrane (for example, by extrusion or by molding, such as injectionmolding) and then sulfonating to produce the dryer polymer substances.This process may be referred to herein as the “blend (dense) route”. Forexample, a poly(vinylidene fluoride)/polystyrene sulfonated acid(PVDF/PSSA) tube may be produced, for example, by:

-   -   i) physically blending PVDF with polystyrene (PS) (or styrene        copolymer) with an addition of a unique compatibilizing agent,        into an essentially homogeneous blend compound;    -   ii) producing a tube by extrusion; and    -   iii) applying a sulfonation process to produce a PVDF/PSSA dryer        tube.

The product may then be washed and dried, for example, for one day.

The PVDF and PS are basically non-miscible materials (materials that donot mix to form a homogeneous solution). An attempt to sulfonate acompound of PVDF and PS failed, probably due to this drawback. It wassurprisingly found that upon adding a suitable compatibilizing agent(such as, poly(methyl methacrylate) (PMMA) or methyl methacrylatebutadiene styrene (MBS)), a PS co-continuous phase was formed andenabled a sulfonation process.

Generally the “blend (dense) route” procedure includes three majorsteps:

-   -   i) mixing of two or more polymers and/or copolymers (such as        PVDF with polystyrene (PS) and/or styrene copolymer such as        styrene-ethylene-butylene-styrene (SEBS)) with a compatibilizing        agent into an essentially homogeneous blend compound;    -   ii) processing the polymer mixture to produce a desired form,        such as a tube, (for example, by extrusion or by molding, such        as injection molding); and    -   iii) applying a sulfonation process to produce a dryer tube.

Reference is now made to FIG. 4, which illustrates a flowchart 400describing a general process of production of a dryer polymer substance.Step 410 includes mixing two or more polymers and/or copolymers whereinat least one of the two or more polymers comprises group(s) capable ofbeing sulfonated (for example, mixing PVDF with polystyrene (PS) and/orstyrene copolymer such as styrene-ethylene-butylene-styrene (SEBS)) witha compatibilizing agent. The mixture may form into an essentially heterophase polymer composition (such as a co-continuous phase structurecomposition). Step 420 includes processing the polymer, for example, byextrusion or by molding (such as injection molding) to produce thedesired structure of polymer substance 430 (for example, a polymer tubeor membrane). Step 460 includes the sulfonation of the group(s) capableof being sulfonated, such as the styrene groups, to produce a dryerpolymer substance 470. Flowchart 400 shows a process for producing adryer polymer substance 470, which may include a dryer tube or amembrane.

Two types of compounds were developed:

-   -   (i) PVDF/PS/PMMA—70/20/10 (70% PVDF/20% PS/10% PMMA),    -   (ii) PVDF/SEBS(KRATON)/MBS (PARALOID compatibilizing        agent)—49/49/2 (49% PVDF/49% SEBS/2% MBS).

The two compounds (a and b) were found to behave as partial-miscibleblends with co-continuous PS phase, which exerted a similar protonexchange function as the PVDP-g-PSSA copolymer mentioned herein. Thesecompounds are easily sulfonated to achieve water vapor pervaporationproperties. The sulfonation may be done, for example, by 0.5M ofchlorosulfonic acid in di-chloroethane for only one hour.

The results carried out on films made from the compounds a and b arepresented in Table 4 below and compared with PVDF and PVDF-g-PSSA films(prior to being converted into a form of pervaporation tubes. The watervapor transmission of PVDF-g-PSSA, 70% PVDF/20% PS/10% PMMA and 49%PVDF/49% SEBS/2% MBS is noticeably better than that of the PVDF.

TABLE 4 Water vapor transmission of different film materials Water vaportransmission Film material [g/A*day] PVDF 22 PVDF-g-PSSA (copolymer 884styranization at 55° C.) 70% PVDF/20% PS/10% PMMA 1000 49% PVDF/49%SEBS/2% MBS 980

After proving the feasibility of the blends' membranes (films), tubeswere produced from 70% PVDF/20% PS/10% PMMA blend and from 49% PVDF/49%SEBS/2% MBS blend. Both blends were processed in an extruder under thesame conditions as the pure copolymer tubes.

Table 5 below shows the performance of the blended tubes, 70% PVDF/20%PS/10% PMMA, 49% PVDF/49% SEBS/2% MBS tubes, compared to the performanceof PVDF-g-PSSA, Nafion® and PVC tubes.

TABLE 5 Performance of the PVDF-g-PSSA, PVDF/PS/PMMA, PVDF/SEBS/MBStubes compared to the performance of the Nafion ® and PVC tubes PVDF-g-PSSA tube PVDF/ PVDF/ PVC (copolymer PS/PMMA SEBS/MBS Test tube Nafion ®at 55°) tube tube Water — 22 260 — — uptake [%] Leak 0 0-10 0-10 0-100-10 [μL/min] ΔCO₂ — 1 1 1 1 Water — 155 260 170 211 evaporation[μL/hour] Vapor 433 151 No 147 125 penetration (282) evidence (285)(308) [μL/hour] of water in (the Δ from the trap PVC)

As shown in Table 5, the following five factors (methods are describedhereinabove) were assessed for each type of tube (PVDF-g-PSSA,PVDF/PS/PMMA, PVDF/SEBS/MBS, Nafion® and PVC tubes):

-   -   1. Water uptake [%];    -   2. Leak [micro-liter/minute];    -   3. ΔCO₂ (change in carbon dioxide)    -   4. Water evaporation [micro-litre/hour]; and    -   5. Water vapor penetration [micro-liter/hour].

These parameters were measured at a temperature of 23° C. and relativeambient humidity (RH) of 50%.

It can be seen from the results detailed in Table 5 that the waterevaporation performance of both the 70% PVDF/20% PS/10% PMMA and the 49%PVDF/49% SEBS/2% MBS tubes was better that that of the Nafion®. Thevapor penetration, and ΔCO₂ performance of the 70% PVDF/20% PS/10% PMMAand the 49% PVDF/49% SEBS/2% MBS tubes were close to that of the Nafion®tube.

It is noted that in the Nafion® case, for example, the viscosity and theprocessing temperature of the copolymer (Teflon® with perfluorovinylether sulfonate) are high (processing temperature about 300° C.). Thislimits the amount of functional groups (such as sulfonic groups) thatcan be added to the copolymer (more sulfonic groups will furtherincrease the viscosity and the processing temperature). According tosome embodiments of the invention, the processing temperature (such asin step 120 in FIG. 1 and step 420 in FIG. 4) may be significantly lessthan 300° C., for example in the range of 180° C.-230° C. According tosome embodiments of the invention, the sulfonation (for example, step160 and step 460 in FIG. 4) is being conducted after the processing (forexample, step 120 in FIG. 1 and step 420 in FIG. 4) and thus the amountof sulfonation is not limited and can reach approximately 100%.

It is also noted that the copolymer (Teflon® with perfluorovinyl ethersulfonate) used for the preparation of Nafion®, even when neutralized,is very reactive (even aggressive) with the processing equipment(particularly with metals). In contrast, the polymers used to producethe dryer polymer substances, according to embodiments of the invention,are substantially non-reactive with the processing equipment.

Mechanical Properties of Gas Dryer Tubes

Table 6 below shows mechanical properties of PVDF/SEBS/MBS tube comparedto the mechanical properties of a Nafion® tube.

The mechanical properties detailed in the table below were taken fromoutput of tensile test carried out on tube samples with an Instronuniversal testing machine according to ASTM D638 at a tension rate of 25mm/min. All values in the table are normalized for purposes ofcomparison.

TABLE 6 mechanical properties of blend (dense) route tube compared tothe mechanical properties of a Nafion ® tube. Ultimate tensile YoungModulus Ultimate elongation Tube sample type strength [MPa] [MPa] [%]Nafion ® tube 20.2 152.8 81 PVDF/SEBS/MBS 18.5 105.6 93 ‘Dens-blend’tube

It can be seen from Table 6 that the mechanical properties of the‘Dens-blend’ tube are on the same order of magnitude as those of theNafion® tube. As described herein, the mechanical properties of thetube, according to some embodiments, can be improved, for example, bymolding support regions, and/or reinforcement element(s) (such as ribs)together with the tube. The support regions may structurally support thetube.

C) Dryer Polymer Substance—the “Porous Route”

According to some embodiments, the present invention provides a robust,high-performance substance (such as a membrane or a tube) designed forthe selective removal of a polar fluid, such as water, from less polargases, such as air and CO₂, by a pervaporation process. According tosome embodiments, such substance (which can be referred to herein as adehydration substance or a dryer substance) may include a compositemembrane that comprises a support member, generally a support polymermember (such as a support membrane or a support tube) in which isincorporated a cross-linked copolymer that has both positively andnegatively charged functionality in a controlled ratio to give thedesired selectivity and flux. By changing the ratio of the chargedgroups and the amount of the copolymer incorporated into the supportmember, the flux and the selectivity can be controlled for use inspecific applications.

It is noted that the terms “membrane” and “tube” may be usedinterchangeably. It is also noted that the terms “dehydration” and“drying/dryer” may be used interchangeably.

The terms “cross-link” or “cross-linked” may include, according to someembodiments, a branch point from which distinct chains emanate.

Preferred materials for the support polymer (as the support member) thatcan be used to produce the gas (such as air) dehydration substanceinclude polysulfone (PSU) and polyether sulfone (PES).

In one aspect, the present invention provides a composite membraneincluding:

-   -   (a) a support member that has a plurality of pores (or        micro-channels) extending through the support member, and    -   (b) a cross-linked copolymer comprising (i) a cationic monomer        and an anionic monomer and/or (ii) a zwitterionic monomer, which        cross-linked copolymer fills the pores of the support member,        the cross-linked copolymer having a permeability for a fluid        that is dependent on the polarity of the fluid, wherein the        permeability increases with increasing polarity.

According to some embodiments, the term “anion” or “anionic” may referto a negatively charged ion.

According to some embodiments, the term “canion” or “canionic” may referto a positively charged ion.

According to some embodiments, the term “zwitterion” or “zwitterionic”may refer to a chemical compound capable of carrying both a positive andnegative charge simultaneously. The total net charge of the chemicalcompound may be zero (electrically neutral).

In the composite membrane, according to some embodiments of theinvention, the cross-linked copolymer fills the pores of the supportmember laterally, that is substantially perpendicular to the directionof the flow through the composite membrane. By “fill” is meant that, inuse, essentially all fluid that passes through the composite membranemust pass through the cross-linked copolymer. A support member whosepores contain cross-linked copolymer in such an amount that thiscondition is satisfied is regarded as filled. Provided that thecondition is met that the fluid passes through the cross-linkedcopolymer, it is not necessary that the void volume of the supportmember be completely occupied by the cross-linked copolymer.

In one preferred embodiment, the air dehydration membrane may be aacrylamido-methyl-propane sulfonate (AMPS)-coated polysulfone hollowfiber membrane, or a poly vinyl alcohol-coated polysulfone membrane, ora poly vinyl alcohol-coated polyether sulfone (PES) membrane.

The air dehydration membranes used in accordance with some embodimentsof the present invention achieve the selective removal of water vaporwhile not significantly altering the relative concentrations of oxygenand nitrogen found in the feed stream.

The cross-linked copolymer provides the separating function of thecomposite membrane in pervaporation separations, and the cross-linkedcopolymer typically swells in the presence of a polar solvent such aswater. In some embodiments, the cross-linked copolymer is a hydrogel.The support member provides mechanical strength to the cross-linkedcopolymer, and it impedes the swelling of the cross-linked copolymerwhen the cross-linked copolymer is swellable.

Preferably, the cross-linked copolymer is anchored within the supportmember. The term “anchored” is intended to mean that the cross-linkedcopolymer is held within the pores of the support member, but the termis not necessarily restricted to mean that the cross-linked copolymer ischemically bound to the pores of the support member. The cross-linkedcopolymer can be held by the physical constraint imposed upon it byenmeshing and intertwining with structural elements of the supportmember, without actually being chemically grafted to the support member,although in some embodiments, the cross-linked copolymer may becomegrafted to the surface of the pores of the support member.

The term “cationic/anionic copolymer” when used herein refers to acopolymer prepared with cationic and anionic monomers. By cationicmonomer is meant a monomer that has a positive charge or a group thatcan be ionized to form a positive charge. Similarly, by anionic monomeris meant a monomer that is negatively charged or that has a group thatcan be ionized to form a negative charge. The performance of thecomposite membrane is mainly determined by the properties of thecopolymer anchored within the pores of the support member. The presenceof both anionic and cationic sites in the copolymer leads to an increasein intramolecular interactions within the copolymer, leading to a morecompact copolymer structure when the copolymer swells in the presence ofa polar fluid. This compact nature helps to increase the selectivity ofcomposite membranes, as it provides a denser copolymer structure throughwhich the fluids must pass. The selectivity of the composite membranesis also enhanced by the presence of the support member, as beyondproviding mechanical strength, the support member also restricts theswelling of anchored copolymer, which again increases the density of thecopolymer.

The anionic monomers used in accordance with some embodiments of thisinvention are preferably water soluble, although anionic monomers thatdisplay little or no solubility in water can be used. Preferred anionicmonomers include unsaturated carboxylic acids or salts or anhydridesthereof, and unsaturated sulfonic acids or salts or anhydrides thereof.Unsaturated anionic monomers may contain one, or more than one,carbon-carbon double bond.

Examples of suitable anionic monomers may include anions comprising asulfonic group such as a sulfonic acid or a salt thereof, such as2-acrylamido-2-methyl-1-propanesulfonic acid,3-allyloxy-2-hydroxy-1-propanesulfonic acid,2-methyl-2-propene-1-sulfonic acid, 2-propene-1-sulfonic acid, styrenesulfonic acid, vinylsulfonic acid. Other examples of anionic monomers(which may or may not be used together with anions comprising a sulfonicgroup) may include, acrylic acid, 2-acetamidoacrylic acid,trans-3-benzoylacrylic acid, 2-bromoacrylic acid, 3-chloroacrylic acid,trans-3-(4-chlorobenzoyl)acrylic acid, 2,3-dichloroacrylic acid,3,3-dichloroacrylic acid, 3,3-dimethylacrylic acid, furylacrylic acid,methacrylic acid, 2-phenylacrylic acid, trans-3-(3-pyridyl)acrylic acid,trichloroacrylic acid, 2-(trifluoromethyl)acrylic acid, propynoic acid(propiolic acid), phenylpropynoic acid, crotonic acid, isocrotonic acid,3-bromo-2-butenoic acid, 2-chloro-2-butenoic acid, 3-chloro-2-butenoicacid, 2,3-dibromo-4-oxo-2-butenoic acid, 2,3-dichloro-4-oxo-2-butenoicacid, 2,3-dimethyl-2-butenoic acid, 2-ethyl-2-butenoic acid,trans-2-methyl-2-butenoic acid (tiglic acid), cis-2-methyl-2-butenoicacid (angelic acid), 4-oxo-4-phenyl-2-butenoic acid, 2-phenyl-2-butenoicacid, 4,4,4-trifluoro-3-methyl-2-butenoic acid, 3-butenoic acid,2-hydroxy-4-phenyl-3-butenoic acid, 2-methyl-3-butenoic acid, 2-butynoicacid (tetrolic acid), 2-pentenoic acid, 4-hydroxy-2-pentenoic acid,2-methyl-2-pentenoic acid (trans), 4-hydroxy-3-pentenoic acid,4-pentenoic acid, 2,2-dimethyl-4-pentenoic acid, 3-methyl-4-pentenoicacid, 2,4-pentadienoic acid, 2-pentynoic acid, 4-pentynoic acid,2-hexenoic acid, 2-ethyl-2-hexenoic acid, 3-hexenoic acid,2-acetyl-5-hydroxy-3-oxo-4-hexenoic acid (dehydracetic acid), 5-hexenoicacid, 2,4-hexadienoic acid (sorbic acid), 1-hexen-1-ylboronic acid,5-hexynoic acid, shikimic acid, 6-heptenoic acid, 2,6-heptadienoic acid,6-heptynoic acid, 2-octenoic acid, trans-1-octen-1-ylboronic acid,fumaric acid, bromo-fumaric acid, chloro-fumaric acid, dihydroxyfumaricacid, dimethylfumic acid, fumaric acid monoethyl ester, mesaconic acid,maleic acid, bromomaleic acid, chloromaleic acid, dichloromaleic acid,dihydroxymaleic acid, dibromomaleic acid, maleamic acid, citraconicacid, glutaconic acid, 3-methyl-2-pentenedioic acid, itaconic acid,muconic acid, mucobromic acid, mucochloric acid, acetylenedicarboxylicacid, styrylacetic acid, 3-butene-1,1-dicarboxylic acid, aconitic acid,3-butene-1,2,3-tricarboxylic acid, 2-acrylamidoglycolic acid,2-sulfoethyl methacrylate, 3-sulfopropyl acrylate, 3-sulfopropylmethacrylate, 3-vinylbenzoic acid, 4-vinylbenzonic acid,tran-2-(4-chlorophenyl)vinylboronic acid,tran-2-(4-fluorophenyl)vinylboronic acid,tran-2-(4-methylphenyl)vinylboronic acid, 2-vinylphenylboronic acid,4-vinylphenylboronic acid, vinylphosphonic acid, monoacryloxyethylphosphate, cinnamic acid, alpha-acetamidocinnamic acid,alpha-bromocinnamic acid, 2-bromocinnamic acid, 3-bromocinnamic acid,4-bromocinnamic acid, 3-bromo-4-fluorocinnamic acid,4-bromo-2-fluorocinnamic acid, 5-bromo-2-fluorocinnamic acid,2-carboxycinnamic acid, 2-chlorocinnamic acid, 3-chlorocinnamic acid(cis), 4-chlorocinnamic acid (trans), 4-chloro-2-fluorocinnamic acid,trans-2-chloro-6-fluorocinnamic acid, trans-2,4-dichlorocinnamic acid,3,4-dichlorocinnamic acid, trans-2,4-difluorocinnamic acid,trans-2,5-difluorocinnamic acid, trans-2,6-difluorocinnamic acid,trans-3,4-difluorocinnamic acid, trans-3,5-difluorocinnamic acid,2,3-dimethoxycinnamic acid, 2,4-dimethoxycinnamic acid,2,5-dimethoxycinnamic acid, 3,4-dimethoxycinnamic acid,3,5-dimethoxycinnamic acid (trans), 3,5-dimethoxy-4-hydroxycinnamicacid, 4,5-dimethoxy-2-nitrocinnamic acid, alpha-ethyl-cis-cinnamic acid,alpha-fluorocinnamic acid, 2-fluorocinnamic acid, trans-3-fluorocinnamicacid, 4-fluorocinnamic acid, 4-formylcinnamic acid, 2-hydroxycinnamicacid, 3-hydroxycinnamic acid, 4-hydroxycinnamic acid,3-hydroxy-4-methoxy-trans-cinnamic acid,4-hydroxy-3-methoxy-trans-cinnamic acid, 4-isopropyl-trans-cinnamicacid, 2-methoxycinnamic acid, 3-methoxycinnamic acid (trans),4-methoxycinnamic acid (trans), alpha-methylcinnamic acid,3,4-(methylenedioxy)cinnamic acid, 4-methyl-3-nitrocinnamic acid,alpha-methyl-3-nitrocinnamic acid, alpha-methyl-4-nitrocinnamic acid,2-nitrocinnamic acid, 3-nitrocinnamic acid (trans), 4-nitrocinnamic-acid(trans), 2,3,4,5,6-pentafluorocinnamic acid, 2-(trifluoromethyl)cinnamicacid, 3-(trifluoromethyl)cinnamic acid,trans-4-(trifluoromethyl)cinnamic acid, 2,3,4-trifluorocinnamic acid,3,4,5-trifluorocinnamic acid, 3,4,5-trimethoxycinnamic acid (trans),2,4,6-trimethylcinnamic acid (cis), and their corresponding anhydride orsalt.

The cationic monomers are also preferably water soluble, althoughcationic monomers that display little or no water solubility can also beused. Cationic monomers can be positively charged, or they can beargroups such as amines that are partially protonated in water to formammonium groups. Preferred cationic monomers include unsaturated aminesand unsaturated ammonium salts. Unsaturated cationic monomers maycontain one, or more than one, carbon-carbon double bond.

Examples of suitable cationic monomers may include cations having a anammonium group (NH₄ ⁺) (or a salt or a derivative thereof), such as4-vinylaniline, 3-(acrylamidopropyl)trimethylammonium salt,(2-(acryloyloxy)ethyl](4-benzoylbenzyl)dimethylammonium salt,[2-(acryloyloxy)ethyl]trimethylammonium salt, diallyldimethylammoniumsalt, [3-(methacrylamido)propyl]trimethylammonium salt,[2-(methacryloyloxy)ethyl]trimethylammonium salt, propargyaminechloride, vinylbenzyltrimethylammonium salt. Other examples of cationicmonomers (which may or may not be used together with cations having a anammonium group) may include, allylamine, N-allylaniline,allylcyclohexylamine, allylcyclopentylamine, allylmethylamine,N-acryloyltris(hydroxymethyl)methylamine,N-tert-amyl-1,1-dimethylallylamine,N-tert-amyl-1,1-dimethylpropargylamine, diallylamine,3,3′-diallyl-oxy-diisopropanolamine, 1,1-diethylpropargylamine,N-ethyl-2-methylallylamine, 3-ethynylaniline, 4-ethynylaniline,1-ethynylcyclohexylamine, geranylamine, N-methylallylamine,propargyamine, vinylamine,(2-(acryloyloxy)ethyl](4-benzoylbenzyl)dimethylammonium salt,[2-(acryloyloxy)ethyl]trimethylammonium salt, 2-aminoethyl methacrylatehydrochloride, N-(3-aminopropyl)methacrylamide hydrochloride,2-(N,N-dimethylamino)ethyl acrylate dimethyl salt,2-(N,N-dimethylamino)ethyl acrylate methyl salt,2-(N,N-dimethylamino)ethyl methacrylate dimethyl salt,2-(N,N-dimethylamino)ethyl methacrylate methyl salt,ethyl-3-amino-3-ethoxyacrylate hydrochloride, 4-ethynylpyridinehydrochloride, and N-2-vinyl-pyrrolidinone.

The molar ratio of anionic monomer to cationic monomer in thecross-linked copolymer is preferably in the range of from 95:5 to 5:95,more preferably in the range of from 1:9 to 1:1, and the ratio ofanionic monomer to cationic monomer is particularly preferable in therange of 1:9 to 1:3. By changing the mole ratio of anionic monomer tocationic monomer, the performance of the composite membrane can bechanged.

The anionic/cationic nature of the copolymer can also be obtained byusing zwitterionic monomers to form the cross-linked copolymer. Thezwitterionic monomers can bear both anionic and cationic groups, or theycan bear groups that can be ionized to form negative and positivecharges. Preferred zwitterionic monomers include unsaturated zwitterionsor precursors thereof that can be readily converted to zwitterions.Unsaturated zwitterionic monomers may include one, or more than one,carbon-carbon double bond.

Examples of suitable zwitterionic monomers include 4-imidazoleacrylicacid, 4-aminocinnamic acid hydrochloride, 4-(dimethylamino)cinnamicacid, 1-(3-sulfopropyl)-2-vinylpyridinium hydroxide inner salt,3-sulfopropyldimethyl-3-methacrylamidopropylammonium inner salt, and5-amino-1,3-cyclohexadiene-1-carboxylic acid hydrochloride. Zwitterionicmonomers can also be used in conjunction with an anionic monomer, with acationic monomer, or with both.

While it is preferable that the support member be hydrophilic tofacilitate the introduction of a charged cross-linked copolymer and tofacilitate the passage of polar fluids, hydrophobic support members canalso be utilized in certain situations, such as when a surfactant or amixed solvent containing water and an organic solvent which wets thesupport member are utilized. Materials that are suitable for furtherhydrophilization to produce a hydrophilic support member include, forexample, cellulose acetate (CA), poly(vinylidene floride) (PVDF),polysulfone (PSU), polyether sulfone (PES), Nylon 6,poly(ethylene-co-vinyl alcohol) (EVAL) and poly(acrylonitrile) (PAN).Materials that are suitable for making a hydrophobic support memberinclude, for example, polypropylene, poly(tetrafluoroethylene) (PTFE)and poly(vinylchloride) (PVC).

The average pore diameter of the support member can vary widely.According to some embodiments, the average pore diameter may range fromabout 0.001 to about 20 microns, for example, from about 0.002 to about5 microns and particularly from about 0.005 to about 1 microns. Theporosity of the support member, which is a measure of the pore volume(also referred to as the void volume), may range, according to someembodiments, from about 25 to about 95%, for example, from about 45 toabout 85% and particularly from about 0.60 to about 80%. Compositemembranes prepared with support members having less than 25% porositymay have low fluxes, while support members with porosity higher than 95%usually do not provide enough mechanical strength to anchor thecopolymer.

The support member used, in accordance with some embodiments may eitherbe a symmetric porous membrane or an asymmetric porous membrane.Microfiltration membranes are suitable as symmetric porous membranes,and they preferably have a thickness of from about 10 to 300 microns,more preferably from about 20 to 150 microns, and particularly from 50to 120 microns. The thinner the support member, the higher the flux.

The asymmetric support member normally has a multi-layered nature, witha dense layer having smaller pores being supported on a backing layerthat has larger pores. Ultrafiltration membranes are suitable for use asasymmetric support members. While these support members are described ashaving “layers”, they only comprise a single continuous phase of asingle polymer. The layers represent regions having different physicalcharacteristics but the same chemical characteristics. The asymmetricmembranes can also comprise non-woven materials (e.g. polyester) whichact as mechanical strengthening materials. For asymmetric supportmembers, the thickness of each layer may not critical, as long assufficient mechanical rigidity is retained. Therefore, in asymmetriccomposite membranes, the void volume of the support member may not befully occupied by the cross-linked copolymer. When the compositemembrane in accordance with some embodiments of the invention isprepared with an asymmetric support member, the thickness of the denselayer determines the flux of the membranes. It has been observed thatasymmetrically filled composite membranes, such as those obtained usingultrafiltration membranes as the support member, lead to pervaporationmembranes having higher fluxes.

Asymmetric composite membranes can also be prepared with symmetricsupport members, by asymmetrically filling the pores of the supportmember with the cross-linked copolymer. Such asymmetric compositemembranes can be prepared by initiating the cross-linking reaction on asingle side of the support member, thus obtaining unequal distributionof cross-linked copolymer through the thickness of the support member.

Production of Cross-Linked Copolymer within a Support Member.

The production of the cross-linked copolymer within a support member (acomposite membrane) may include the following steps, in accordance withsome embodiments of the invention:

-   -   i. Preparation of the porous support member;    -   ii. Surface-activation;    -   iii. Impregnation of monomers solution into the porous support        member;    -   iv. Graft co-polymerization of the monomers; and    -   v. Cross-linking.

a. Preparation of the Porous Support Member:

Polymeric support members may be produced by any method known in theart. Washing the obtained polymeric support member with water or watersolutions is performed in order to extract (remove) water-solublepolymers that are present in the pores of the polymeric support memberand produce the desired porous support members. This washing orextraction step thus clears the pores from undesired impurities (such ashomopolymer).

Surfactant-type chemicals (such as any commercially known chemicalsurfactants for example, Triton, Tetronic, Pluronic, and Softanol) mayalso be used to better clear the pores. Other surfactants may be used,for example, low molecular weight surfactants such as sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS). Otherconventionally used treating materials may also be used for moreefficiently clearing the pores; such materials may include low molecularweight alcohols, such as isopropanol (IPA) and ethanol, and solventssuch as Freon (chlorinated hydrocarbons). According to some embodiments,the porous support member may be manufactured for the purpose orcommercially available.

b. Surface-Activation:

After producing the porous support member, a step of surface-activationmay be required. The surface-activation step affects the surface of thesupport member and/or the surface of the pores of the porous supportmember. The surface-activation is adapted to facilitate the adhesion ofthe polar monomers (such as cation and anion monomers/zwitterion that islater polymerized and cross-linked to form the co-polymer pore “filler”)to the pores (more precisely to the surface of the pores) of the poroussupport member. This step is particularly required when the poroussupport member is of hydrophobic nature (such as PES). According to someembodiments, the surface-activation step includes oxidation and isadapted to introduce carbonyl groups (which are capable of binding tothe monomers) to the polymer porous support member.

When hydrophobic porous support members (such as PES) are used, thesurface-activation step may be referred to as hydrophilization (or“wetting”) of the porous support member to increase the adhesion of thepolar monomers. Hydrophilization may be performed by oxidation.Oxidation may be accomplished by any appropriate reagent such asammonium persulfate, or any other oxidation agents. Other oxidationmethods may include ozone treatment, ultraviolet light irradiation,corona discharge, high-voltage electric discharge, plasma treatment orany other method.

Surfactants (such as those mentioned herein) may also be used in thehydrophilization step to improve the results.

c. Impregnation of Monomers Solution into the Porous Support Member:

After surface-activating the porous support member, the step ofimpregnation of the monomers solution into the porous support member isperformed. This step includes physically introducing to the poroussupport member a solution containing the cation and anionmonomers/zwitterion solution that will later be polymerized andcross-linked to form the co-polymer pore “filler”. This solution may bereferred to as a pre-polymerized polymer precursor solution. Thesolution may also include an electrolyte polymer, a polymerizationinitiator, a cross-linker or any other appropriate additive.

According to some embodiments, ultrasonic energy may be applied tofacilitate impregnation.

Conditions for the impregnation step, such as temperatures and/or times,are selected by considering the form or shape of the porous supportmember to be treated.

In cases where the porous support member is a tube (a hollow fiber) theimpregnation step may be accomplished by using a pump, such as aperistaltic pump, to “force” the solution into the tube and into thepores. Another way to facilitate the penetration of the impregnants intothe pores is by cutting the tube to a few centimeters length prior toperforming the impregnation.

d. Graft Co-Polymerization of the Monomers:

Once the solution containing the cation and anion monomers/zwitterion(and any other required additives) is physically introduced to theporous support member, the step of graft co-polymerization is performed.This step includes the formation of chemically bonding the monomers tothe porous support member and co-polymerizing the monomers to produce aco-polymer, which is chemically bound and anchored in place within thepores of the support membrane.

For example, chemical grafting of a PES porous member can be describedas a process consisting of surface-activating of the PES porous member,attaching monomers to the reactive sites followed by (or at the sametime) polymerization, whereby polymer branches are formed such that theyare attached to the main PES polymer. The chemical grafting may becarried out by the abstraction of a hydrogen atom from the hydroxylgroup of PES. PES has active labile hydrogen atoms, which can besurface-activated in the presence of a graft initiator, giving rise tofree radicals. The free radicals thus produced in the process initiategraft co-polymerization. The series of reaction steps involved in graftco-polymerization of a porous member may be as follows: The graftinitiator ion starts the action and the whole process behaves like anautocatalytic one. A small amount of graft initiator ion (such as 10-100ppm) may therefore be sufficient to carry out the process of graftco-polymerization. The foregoing reactions may take place in thepresence of peroxide, which concurrently regenerates the graftinitiator, forming a free radical.

The graft initiator may consist of a metal ions system such as Fe³⁺,Fe²⁺, Ag⁺, Co²⁺ or Cu²⁺. The peroxide may be chosen from thewater-soluble catalysts, such as hydrogen peroxide, urea peroxide,ammonium persulfate, potassium persulfate and/or sodium metabisulfite.The monomers and pre-polymers have side functional groups, which mayreact between themselves and with additional pre-polymers included intothe formulation, forming a graft co-polymer.

The initiation of the co-polymerization may be carried out withwater-soluble redox initiator combinations customary for emulsionpolymerization.

A redox initiating agent may be formed by a combination of theabove-mentioned peroxides and a reducing agent, such as a sulfite, abisulfite, a thiosulfate, formamidinesulfinic acid, and/or ascorbicacid. For example, polymerizations may be conducted in an aqueousemulsion using ammonium persulfate or ammonium persulfate/sodium sulfiteredox initiation.

Other or additional polymerization systems may be applied, such asthermal or UV-based polymerization systems, “living” or controlledpolymerization, step-growth polymerization, chain-growth polymerizationor any combination thereof, or any other polymerising system.

It is also possible to use generally known regulators for theco-polymerization, for example amines (for example, triethylamine,tripropylamine or tributylamine), halogen compounds (for example,chloroform, carbon tetrachloride or carbon tetrabromide), mercaptans(for example, 1-butanethiol, 1-hexanethiol, 1-dodecanethiol, ethyldisulphide, phenyl disulphide or butyl disulphide), alcohols (forexample, ethanol, n-/iso-propanol or n-/iso-/tert-butanol),mercaptosilanes or sulphur silanes).

To reduce the viscosity, it is possible to use solvents, for example,aromatic hydrocarbons (for example, toluene, xylene, and so forth),esters (e.g. ethyl acetate, butyl acetate, amyl acetate, cellosolveacetate, etc.), ketones (for example, methyl ethyl ketone, methylisobutyl ketone, diisobutyl ketone, and so forth), and so forth. Thesolvent can be added during the course of the free-radicalpolymerization. Esters having a branched alcohol radical give polymershaving a reduced solution viscosity.

e. Cross-Linking:

The function of cross-linking is to control and modulate flexibility ofthe cross-linked copolymer. According to some embodiments, thecross-linking of the co-polymer hardens the co-polymer (for example,converts it from liquid to gel form) and prevents it from leaking out ofthe pores. Cross-linking of the co-polymer within the support member canbe conducted after or during the co-polymerization. The cross-linkingagents used may be highly reactive, have low volatility and have atleast two unsaturated groups to form a three dimensional cross-linkedstructure with the cationic/anionic copolymer.

While water-soluble cross-linking agents are preferred, cross-linkingagents that display little or no solubility in water can also be used.Examples of suitable cross-linkers include3-(acryloyloxy)-2-hydroxypropyl methacrylate, allyl diglycol carbonate,bis(2-methacryloxyethyl)phosphate, 2,2-bis(4-methacryloxyphenyl)propane,2,2-bis[4-(2-acryloxyethoxy)phenyl]propane,2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane,1,4-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanedioldimethacrylate, cinnamyl methacrylate, 2-cinnamoyloxyethyl acrylate,trans-1,4-cyclohexanediol dimethacrylate, 1,10-decanedioldimethacrylate, N,N′-diallylacrylamide, diallyl carbonate, diallylmaleate, diallyl phthalate, diallyl pyrocarbonate, diallyl succinate,1,3-diallylurea, 1,4-diacryloylpiperazine, diethylene glycol diacrylate,diethylene glycol dimethacrylate, diethylene glycol divinyl ether,2,2-dimethylpropanediol dimethacrylate, dipropylene glycoldimethacrylate, divinyl glycol, divinyl sebacate, divinylbenzene,N,N′-ethylene bisacrylamide, ethylene glycol diacrylate, ethylene glycoldimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanedioldimethacrylate, N,N′-hexamethylenebisacrylamide,N,N′-methylenebismethacrylamide, 1,9-nonanediol dimethacrylate,pentaerythritol tetraacrylate, pentaerythritol triacrylate,pentaerythritol triallyl ether, 1,5-pentanediol dimethacrylate,1,4-phenylene diacrylate, tetraethylene glycol dimethacrylate, triallylcyanurate, triethylene glycol diacrylate, triethylene glycoldimethacrylate, triethylene glycol divinyl ether,1,1,1-trimethylolpropane diallyl ether, 1,1,1-trimethylolpropanetriacrylate, and 1,1,1-trimethylolpropane trimethacrylate.

The amount of cross-linking agent may be from 0.1% to 25%, for example,from 0.5% to 20%, and particularly from 1.0% to 15%, based on the totalmolar amount of monomers.

Reference is now made to FIG. 5, which shows a flowchart 500 summarizinga general process of production of a dryer polymer substance, accordingto some embodiments. Step 510 includes obtaining a porous polymersubstance (porous support member), for example, a polyether sulfone(PES) porous tube. Polymeric support members may be produced by anymethod known in the art. This step may include washing the obtainedpolymeric support member with water or water solutions, performed inorder to extract (remove) water-soluble polymers that are present in thepores of the polymeric support member and produce the desired poroussupport members. Step 520 includes surface-activation of the supportmember and/or the surface of the pores of the porous support member. Thesurface-activation is adapted to facilitate the adhesion of the polarmonomers (such as cation and anion monomers/zwitterion that is laterpolymerized and cross-linked to form the co-polymer pore “filler”) tothe pores (more precisely to the surface of the pores) of the poroussupport member. Step 530 includes impregnation (introduction) into theporous support member of a solution comprising: (i) a cationic monomerand an anionic monomer, (ii) a zwitterionic monomer, or a combination of(i) and (ii). This step may also be performed, for example, by coatingmethodologies and/or by impregnation techniques. Step 540 includes graftco-polymerization of the anionic monomer and the cationic monomer and/orthe zwitterionic monomer. Step 550 includes cross-linking to form across-linked copolymer that at least partially fills the pores of thesupport member to produce the final dryer polymer substance 560 (acomposite membrane/tub) which is adapted to exhibit water pervaporationproperties.

EXAMPLES

The following examples are provided to illustrate the invention. It willbe understood, however, that the specific details given in each examplehave been selected for purpose of illustration and are not to beconstrued as limiting the scope of the invention. Generally, theexperiments were conducted under similar conditions unless noted.

In the specific examples that follow, the support member was obtainedfrom the Hydranautics Corporation.

This hollow fiber (support member) is commercially available, and issold under the trademark HYDRACAP.

The hollow fiber has been used for water purification processes, and iscategorized as a UF (ultrafiltration) membrane of Hydranautics Corp. Thefiber is made of polyether sulfone (PES), Nominal MWCO, Daltons 150,000.The hollow fiber has an outside diameter of 1.2 mm. The hollow fiberused in these examples is porous and hydrophobic, and has essentially noselectivity between oxygen and nitrogen.

Materials Used for Graft Co-Polymerization Anionic Monomers ContainingSulphonic Acid Sites:

AMPS 2-acrylamido-2-methyl-1-propanesulfonic acid Sodium salt, LubrisolAMPS 2404 AMPS 2405 NaSS 4-styrene sulfonic acid, sodium salt, Tosoh

Cationic Monomers Containing Ammonium Sites for Copolymerization:

APTAC 3-(acrylamidopropyl)trimethylammonium chloride, Aldrich AETAC[2-(acryloyloxy)ethyl]trimethylammonium chloride MAETAC[2-(methacryloyloxy)ethyl]trimethylammonium chloride DMAEA2-(N,N-dimethylamino)ethyl acrylate 4-imidazoleacrylic acid(zwitteronic)

Polyunsaturated Crosslinking Monomers

MBAA N,N′-methylenebismethacrylamide. Aldrich N,N′-bismethylol methylenebisacrylamideFree radical initiators (peroxides) include inorganic persulfate,peroxides, and redox (APS+NaBS)

Ammonium ammonium peroxydisulfate, initiator, Aldrich persulfate, 98%disodium disulfite and disodium pyrosulfite initiator, Sodium Aldrichmetabisulfite, 97% hydrogen peroxideFree radical initiators include organic hydro peroxide; azo

Luperox P Tert-butyl peroxy benzoate, Arkema VAZO 442,2′-azobis(2-(4,5-dihydroimidazolyl)propane), Du Pont VAZO 562,2′-azobis(2-methylpropionamidine) dihydrochloride VAZO 684,4′-azobis(4-cyanovaleric acid) VAZO 881,1′-azobis(cyclohexanecarbonitrile) AIBN 2,2′-azobisisobutyronitrile

Catalyst-Surfactant SO₃H Moieties:

Cycat 4040 paratoluene sulfonic acid, catalyst for low temperaturereactions

Monounsaturated Silanes

MEMO Methacryloxypropyl-trimethyoxysilane MAPTOS, Evonik VTMOvinyl-trimethoxysilane

Polyfunctional Crosslinking Silanes

TEOS Tetraethoxyorthosilicate, Evonik GLYMOGlycidoxypropyl-trimethyoxysilane AMEO 3-Aminopropyltriethoxy silaneDAMO Gamma-aminopropyl-triethoxysilane

Example 1

Surface of PES fiber was washed for 30 minutes at RT using 5% ethanol insolution. Hydrophilization (activation) of the porous support member wasperformed using ammonium persulfate 0.1%.

After undergoing the above-described treatment, the resultant membranewas cooled to ambient temperature, washed with water for about 10 toabout 20 minutes in order to remove the remains of oxidizer, and thendried at about 70° C. for about 40 minutes.

Solution for the impregnation step prepared from cationic monomer was[2-(methacryloxy)ethyl]trimethylammonium chloride (MAETAC), the anionicmonomer was sodium salt 2-acrylamido-2-methylpropanesulfonic acid,N,N′-methylenebisacrylamide (MBAA). Their mole ratio was 1000:800:75.

Ammonium persulfate and Na hydrogensulfite were used as the redoxinitiators, Luperox P was used as free-radical copolymerizationinitiator—its mole ratio was 0.75:0.04:7.5 on total amount of monomers.

Mixing the above chemicals and diluting them to 50% monomersconcentration, stirring the mixture for 0.5-2 hrs until all solids aredissolved in water. The monomer mixture can be added a little at a timeor continuously. This allows the evolution of heat to be controlled.

After filtration to remove any undissolved solid by filter paper, themixture was ready to prepare the membrane. The concentration of themonomers in the solution was 60 wt. %.

The porous membrane was subsequently immersed (impregnated) in a polymerprecursor solution comprising of 2-acrylamido-2-methylpropanesulfonicacid, of N,N′-methylenebisacrylamide, radical polymerization initiator,isopropyl alcohol and water, thus filling (impregnating) the membranewith the solution.

Subsequently, the porous substrate was pulled out of the solution. Afterhollow fiber immersion and removing the excess solution, the membranewas put into an oven at 80° C. (graft co-polymerization), for between0.5 to 1 hours, until the co-polymerization reaction finished.Cross-linking was performed at 90-110° C.

Example 2

Example 2 illustrates a method for surface-activation of the tubing.Surface of PES fiber is washed to remove some impurities with anappropriate liquid.

Hydrophobic PES membrane is provided with a permanent hydrophilicsurface made by depositing a water/alcohol solution for 10 minutes asthe impregnation step. Solution 5% ethanol is used to wash the membranefor 30 min at RT.

Once the porous hydrophobic PES membrane was obtained, it washydrophilized as follows:

A sample of hydrophobic PES membrane (about 6 cm length) was prewettedin isopropyl alcohol (IPA), washed with DI water.

Membrane is immersed in an aqueous solution of oxidizer (ammoniumpersulfate). The concentration of ammonium persulfate (APS) was about0.1-3%. The solution was heated from ambient to about 90-95° C. forabout 15 minutes. After undergoing the above described treatment, theresultant membrane was cooled to ambient temperature, washed with waterfor about 10 to about 20 minutes in order to remove the remains ofoxidizer and then dried at about 70° C. for about 40 minutes. Animpregnation solution was prepared as in Example 1 as well as the stepsof impregnation, graft co-polymerization and cross-linking.

Example 3

Reference is now made to FIG. 6, which shows a scheme describing anexample of a process protocol of production of a dryer tube according tosome embodiments. Step 1 includes obtaining a polymeric porous tube, inthis case a PES porous tube and coating it with another substance inorder to introduce a compound having sulfonic acid moieties into aninfrastructure of the porous polymer tube. In this case, coating isperformed by immersing the PES porous tube in a solution ofacrylamido-methyl-propane sulfonate (AMPS) for 10 minutes to produce aPES tube coated and filled with AMPS. In Step 2, the PES tube, which iscoated and filled with AMPS, is surface-activated by using potassiumper-sulfate or peroxide for one hour at 50° C. to produce a PES tubehaving polymerized AMPS. In Step 3, the PES tube having polymerized AMPSis cross linked for 1 hour at 80° C. and washed and dried to produce aPES-g-AMPS cross-linked membrane tube.

Example 4

Table 7 below shows the performance of the porous route tubes, accordingto some embodiments of the invention, compared with the performance ofthe Nafion® tube. The first example refers to a PES porous hollow-fibertube pre-treated with 0.1 wt % of Ammonium per-sulfate oxidizing agentin a surface-activation alcoholic solution, and the second examplerefers to a PES porous hollow-fiber tube pre-treated with 1.0 wt % ofAmmonium per-sulfate oxidizing agent in a surface-activation alcoholicsolution.

TABLE 7 Performance of the first and second examples porous route tubescompared to Nafion ® tube. First Second example example porous porousTemperature RH route route Test [c.] [%] tubes tubes Nafion ® Leak 23 550 10.08 0 [μL/min] ΔCO₂ 23 55 1 1 0 Water 23 55 145.2 155.4 124.8evaporation [μL/hour] Vapor 22 34 200 100 155 penetration [μL/hour]

In the vapor penetration test, a leak test has been taken every hour.The new PES membrane shows stable air leak behavior during the 4-hourtest procedure.

As shown in Table 8, the following four factors were assessed for eachof the first and second examples of porous route tubes and compared tothe Nafion® tube:

-   -   1. Leak [micro-liter/minute];    -   2. ΔCO₂ (change in carbon dioxide)    -   3. Water evaporation [micro-liter/hour]; and    -   4. Water vapor penetration [micro-liter/hour].

These four factors were tested at the specified temperature [° C.] andrelative ambient humidity (RH) [%].

It was surprisingly found that the water evaporation performance of thefirst and second examples of porous route tubes was higher than that ofNafion®.

The following is a discussion of the physical mechanisms believed tounderlie the operation of the dehydration membranes used herein.However, the invention should not be deemed limited by the followingexplanation.

It is believed that air and water vapor pass through the dehydrationmembrane used herein, according to some embodiments, by three differentmeans.

For water vapor penetration, the relevant mechanisms may be:

-   -   1) permeation through the dense polymer;    -   2) viscous flow through the pores; and    -   3) knudsen flow through the very fine pores.

The permeation through the dense polymer is believed to be the dominantfactor for water vapor penetration.

The dryer polymer substance (such as a tube) may be prepared, accordingto some embodiments, by obtaining a porous polymer tube, cutting intotubes having a desired length (for example, 50 mm) and introducing tothe cut porous polymer tubes compound(s) having sulfonic acid moieties(such as in step 520). This may be followed by polymerizing (such as instep 520) and cross-linking (such as in step 520).

The dryer polymer substance (such as a tube) may be prepared, accordingto alternative or additional embodiments, by obtaining a porous polymertube, introducing to the tubes compound(s) having sulfonic acid moieties(such as in step 520), polymerizing (such as in step 520) andcross-linking (such as in step 520). The tube may then be cut into tubeshaving a desired length (for example, 50 mm). Since this order ofactions involves treatment of a relatively long tube, there may be aneed to use a pump (such as a peristaltic pump) to facilitate thesolution penetration into the tube (and/or air, for example, to removethem) and thus improve the homogeneity of the built-up internal coating.

According to some embodiments, part of the treatment (for example,introduction of compound(s) having sulfonic acid moieties) may beperformed on a pre-cut tube and another part of the treatment (forexample, polymerizing and cross-linking) on a cut tube.

According to some embodiments, the polymer substance may be formed insuch ways that allow improving pervaporation, while also improvingmechanical properties of the substance. Examples of improved polymersubstances and methods of producing same are described in the followingparagraphs.

According to some embodiments, coating and/or impregnation and/orgrafting of the porous tube may be performed in specific areas of thetube, while other areas may remain un-grafted/uncoated/un-impregnated(for example, but not limited to, by blocking arrears of the porous tubewhere grafting/coating/impregnation is not desired). Accordingly, thepolymer substances (such as a tube) covered under the scope of someembodiments of this invention, may include a polymer substance thatcomprises impregnated areas (for example, by AMPS and un-impregnatedareas). This may allow, for example, control of the pervaporationperformance of a dryer polymer substance, but may be used for any otherapplication.

According to some embodiments, the infrastructure of a porous polymersubstance (such as a tube or membrane) may be asymmetric, for example,the pores could be larger on one surface of the porous polymer substance(for example, on the outer surface of a tube) and more dense (and/orsmaller) on the other surface of the porous polymer substance (forexample, inside the tube), Accordingly, the infrastructure of the porouspolymer substance can be coated, grafted or impregnated on one surfaceand not (or less) coated, grafted or impregnated on the other surface.Such a structure can provide, on the one hand, good and fastpervaporation properties (only a thin sulfonated wall to pass through)but much better mechanical strength (the area with the larger poresaffect only the mechanical strength of the tube but not thepervaporation).

Another example of an asymmetric porous polymer substance, according tosome embodiments, may be a porous polymer tube having larger pores onone or two ends of the tube and more dense pores on the inner part ofthe tube. The porous tube can thus be coated/grafted or impregnated onthe inner part and not (or less) coated/grafted or impregnated on theends. Such a structure can provide pervaporation properties in the innerpart of the tube while the ends of the tube (where no evaporationfunctionalities are required) may be used to connect to other parts of atubing system (for example, a breath sampling system).

According to some embodiments, the thickness of a wall of a dryerpolymer tube (produced by the “grafting (dense) route”, the “blend(dense) route”, the “porous route” or by any other method as disclosedherein may be over 130 micrometers, for example over 150 micrometers, inthe range of 130-200 micrometers, in the range of 150-300 micrometer, inthe range of 200-400 micrometers or over 400 micrometers.

Example 5 Mechanical Properties of Gas Dryer Tubes

The ‘Porous-coating’ tube cannot be directly compared to the Nafion®tube since its basic matrix is not a continuous morphology, as in theNafion® and in the blend and grafted types of tubes.

It was established that the ‘Porous-coating’ tube is more flexible andless prone to kinking and/or collapsing compared to the Nafion® tube.

According to some embodiments, the porous type tube can be made thicker(as the pores are completely filled with pervaporating material)compared to the Nafion® tube. In addition, the pores' size and densitycan be controlled during the manufacturing of the tube and, therefore,the mechanical properties and pervaporation performance can beoptimized.

Exemplary Implementations of Dryer Polymer Tubes

According to some embodiments, the dryer polymer tubes (produced in anyprocess, such as but not limited to, by the “grafting (dense) route”,the “blend (dense) route” and the “porous route”) may be in variousforms and shapes. A certain shape may be selected to affect themechanical properties (such as strength, kinking or any other property)of the tube as well as the pervaporation capabilities thereof.

Reference is now made to FIGS. 7 a-d, which show exemplary tubes, havingdifferent shapes, according to some embodiments. FIG. 7 a shows a dryertube 700

having three areas, end areas 702 and 704 and central area 706. Theexternal diameter of end areas 702 and 704 is d1, and the externaldiameter of central area 706 is d2. In this case, d1 is larger than d2.The internal diameter d3 of all areas of dryer tube 700 is the same.Such tube may be used for example to allow desired pervaporationperformance in central area 706 and structural strength (with or withoutpervaporation performance) in end areas 702 and 704.

FIG. 7 b shows, according to some embodiments, a ribbed dryer tube 710having, along the length of the tube, an essentially constant internaldiameter d4 and two external diameters d5, in the lowered areas 712, andd6 in the elevated areas 714. Elevated areas 714 which extend along thelength of the tube may also be referred to as “ribs” which may increasethe strength of dryer tube 710. Other types or forms of ribs may also beformed or used. Such ribs may include spiral ribs (not shown),concentric ribs (not shown), or other ribs having any kind of pattern.Tube 710 has an inner conduit 715 adapted to allow a flow of a gas. Theinternal cross section of the tube is shown to be circular, having adiameter of d4; however, according to some embodiments, the internalcross-section of a tube can also match to an external cross-section ofthe tube (which may be non-circular) as shown, for example, in FIG. 7 cwhere the internal and external cross-sections have a star shape (willbe described in detail hereinbelow). Lowered areas 712 and elevatedareas 714 may have similar or different pervaporation performance. Thesefeatures can be accomplished, for example, by injection molding of thetubes. This cannot be accomplished in Nafion®, which will not maintainits functionality and characteristics in the temperatures and stressesinvolved in injection molding.

FIG. 7 c shows, according to some embodiments, a star-shaped dryer tube720 having, along the length of the tube, lowered areas 722 andelevated, pointed areas 724. Elevated areas 724 which extend along thelength of the tube may increase the strength of dryer tube 720. Theinternal cross-section 726 of dryer tube 720 matches the externalcross-section 728 of dryer tube 720. Lowered areas 722 and elevated,pointed areas 724 may have similar or different pervaporationperformance. A non-circular internal cross-section (such as thestar-shaped internal cross-section 726 of dryer tube 720, rectangular,square, pointed, flower shaped or any other non-circular internalcross-section) increases the surface area, and the ability to captureliquids in the corners/conduits (formed inside the tube) withoutblocking the tubing line, and further creating better hydrophillicproperties, spreading the fluids (such as water) along the walls of thetube so that they can be easily absorbed and pervaporated.

The internal and/or external cross-section of any dryer tube, may have,according to some embodiments, a circular or a non-circularcross-section, such as, but not limited to, a star-shaped, rectangular,square, pointed, flower shaped or any other non-circular cross-section).

According to some embodiments, the internal and/or externalcross-section of any dryer tube may be the same or vary along the lengthof the tube.

FIG. 7 d, shows, according to some embodiments, a dryer tube 730 havinga central area 732 and two end areas 734 and 736. Central area 732,which extends between the two end areas 734 and 736, is adapted topervaporate fluid(s) such as water. According to some embodiments, endareas 734 and/or 736 may be separately formed and assembled with centralarea 732. According to some embodiments, end areas 734 and/or 736 may beintegrally formed with central area 732. In the case where areas 734and/or 736 are integrally formed with central area 732, dryer tube 730may be produced according to any method, particularly by molding.According to additional or alternative embodiments, dryer tube 730 (orany other dryer tube according to embodiments of this invention) mayinclude a central area (such as central area 732), which has onlydefined drying zones (or “windows”) such as drying zones 738, 740 a, band c that are adapted to pervaporate fluid(s), wherein the rest of thecentral area (such as central area 732) is not adapted to pervaporatefluid(s), but rather to provide strength or to “hold” the drying zones.The drying zones (such as drying zones 738, 740 a, b and c) may beformed by cutting an area of the central area (such as central area 732)and replacing it with a drying substance (such as a membrane). Thedrying zones may also be formed by activating/chemicallytreating/grafting/solfunating and/or applying any other process tocertain zones of the central area to convert them into fluid dryingzones.

According to some embodiments, in any of the dryer tubes, such as tubes700, 710, 720 and 730 of FIGS. 7 a-d, any process disclosed herein suchas grafting, impregnation, activation, surface activation and/or anyother process, can be performed on the whole tube or only one or moreareas of a tube (such as a central area). The area selective processesmay result in a tube having areas with high pervaporation performanceand areas with less pervaporation performance but better mechanicalproperties.

Reference is now made to FIG. 7 e, which shows an asymmetric porousdryer tube, according to some embodiments of the invention. Porous dryertube 750 (which may also be described to as a porous support memberhaving pores which may be filled/coated/grafted/impregnated, accordingto embodiments of the invention) includes an outer surface 752 and aninner surface 758 (defining an inner conduit 759 extending along thelength of porous dryer tube 750 and adapted for fluid flow). Dryer tube750 also includes two sections: a non-dense section 754 and a densesection 760. Non-dense section 754 is located at the area of outersurface 752 and includes large pores 756. Dense section 760 is locatedat the area of inner surface 758 and includes small pores 762. Whenfluid flows through inner conduit 759 in the direction of the arrow,water and/or water vapors can pervapporate through the small pores 762which are adapted to be filled with a cross-linked co-polymer. Once thewater and/or water vapors passed the small pores 762 they pass,essentially without interruption, though the unfilled large pores 756and exit porous dryer tube 750. It is thus possible to obtain a porousdryer tube (such as porous dryer tube 750) having on one hand arelatively thin dense section 760 facilitating efficient pervaporetionand on the other hand a non-dense section 754 which strengthen the tubewithout affecting the pervaporetion performance.

Reference is now made to FIGS. 8 a-c, which show dryer tubes connectedto tubing systems, according to some embodiments.

FIG. 8 a shows a tubing system 800, which includes a dryer tube 802connected at its first end 803 to a first tube 804 and at its opposingend 805 to a second tube 806. Tube 804 may be used, for example, forcollecting breath from a patient to dryer tube 802, and tube 806 may beused, for example, for passing the dried breath from dryer tube 802 toan analyzer. such as a capnograph or any other analyzer that is adaptedto provide information related to the patient's breath. The arrow showsthe direction of flow in tubing system 800. The external diameter ofdryer tube 802 is smaller than the inner diameters of first tube 804 andsecond tube 806. Thus, first end 803 and opposing end 805 of dryer tube802 can be inserted into tube 804 and tube 806, respectively. First end803 and opposing end 805 of dryer tube 802 can be secured to tube 804and tube 806 by rings 808 and 810, respectively.

FIG. 8 b shows a tubing system 820, which includes a dryer tube 822connected at its first end 823 to a first tube 824 and at its opposingend 825 to a second tube 826. Dryer tube 822, tube 824 and tube 826 maybe used, for example, as described in FIG. 8 a. The external diameter ofdryer tube 822 is smaller than the inner diameters of first tube 824 andsecond tube 826. Thus, first end 823 and opposing end 825 of dryer tube822 can be inserted into tube 824 and tube 826, respectively. First end823 and opposing end 825 of dryer tube 822 can be secured to tube 824and tube 826 by rings (as shown in FIG. 8 a as 808 and 810,respectively). Tubing system 820 also includes a mesh 830, whichpartially covers the external surface area of dryer tube 822. Mesh 830also partially covers the external surface area of end area 832 of tube824 and the external surface area of end area 833 of tube 826. Mesh 830may function as a protective layer to dryer tube 822, for example, toincrease the mechanical strength of the dryer tube 822, if necessary.

FIG. 8 c shows a tubing system 840, which includes a dryer tube 842connected to a tube 844 by a connecting sleeve 843. The externaldiameter of connecting sleeve 843 is smaller than the inner diameters ofdryer tube 842 and tube 844. Dryer tube 842 and tube 844 may be fastenedto connecting sleeve 843 for example, by an adhesive, by heatingconnecting sleeve 843 (particularly if it is made from metal(s)) andthus melting and/or welding dryer tube 842 and/or tube 844, or by anexternal ring (or clip) as shown in FIG. 8 a. A connecting sleeve mayalso have an internal diameter larger than the external diameter of thedryer tube and another tube and connect them by attaching to the tubesfrom their outer surface.

1-46. (canceled)
 47. A dryer polymer substance adapted to pervaporatewater, water vapor or both from a gas while maintaining theconcentration of CO₂, O₂ or both in said gas, the polymer substancecomprising a porous support member comprising polyether sulphone (PES);wherein at least a portion of the support member's pores comprises agrafted cross-linked co-polymer formed from[2-(methacryloxy)ethyl]trimethylammonium chloride (MEATAC),2-acrylamido-2-methyl-1-propanesulfonic acid andN,N′-methylenebisacrylamide (MBAA); wherein when the dryer substance isa dryer tube with an internal diameter of 1.0±0.1 millimeter (mm); anouter diameter of 1.24±0.02 mm and a length of 50 mm, the tube has awater evaporation rate of over 150 micro-liter/hour at a temperature of23° C. and at 55% humidity.
 48. The dryer polymer substance according toclaim 47, wherein the dryer polymer substance is a dryer tube.
 49. Thedryer polymer substance according to claim 48, wherein the dryer tubehas a circular internal cross-section.
 50. The dryer polymer substanceaccording to claim 48, wherein the dryer tube has a circular internalcross-section and a non-circular external cross-section.
 51. The dryerpolymer substance according to claim 48, wherein the dryer tube has anon-circular internal cross-section and a circular externalcross-section.
 52. The dryer polymer substance according to claim 48,wherein the dryer tube has a non-circular internal cross-section and amatching non-circular external cross-section.
 53. The dryer polymersubstance according to claim 48, wherein the porous support membercomprises at least a first section having pores of a first diameter anda second section having pores of a second diameter and wherein the firstdiameter is smaller than the second diameter.
 54. The dryer polymersubstance according to claim 53, wherein the first section is located ator in proximity to an inner surface of the dryer tube and the secondsection is located at or in proximity to an outer surface of the dryertube.
 55. A dryer polymer substance adapted to pervaporate water, watervapor or both from a gas while maintaining the concentration of CO₂, O₂or both in said gas, the polymer substance comprising a porous supportmember; wherein at least a portion of the support member's porescomprises a grafted cross-linked co-polymer; wherein the porous supportmember comprises at least a first section having pores of a firstdiameter and a second section having pores of a second diameter andwherein the first diameter is smaller than the second diameter; whereinthe first section is located at or in proximity to an inner surface ofthe dryer tube and the second section is located at or in proximity toan outer surface of the dryer tube.